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29  CEREBROSPINAL, SYNOVIAL, SEROUS BODY FLUIDS, AND ALTERNATIVE SPECIMENS
Donald S. Karcher, Richard A. McPherson
CHAPTER
CEREBROSPINAL FLUID, 480
Specimen Collection and Opening 
Pressure, 481
Indications and Recommended 
Tests, 481
Gross Examination, 481
Xanthochromia, 482
Differential Diagnosis of 
Bloody CSF, 482
Microscopic Examination, 482
Total Cell Count, 482
Differential Cell Count, 483
Chemical Analysis, 485
Proteins, 485
Glucose, 489
Lactate, 489
F2-Isoprostanes, 489
Enzymes, 489
Ammonia, Amines, and Amino 
Acids, 490
Electrolytes and Acid-Base 
Balance, 490
Tumor Markers, 490
Microbiological Examination, 490
Bacterial Meningitis, 490
Spirochetal Meningitis, 491
Viral Meningitis, 491
Human Immunodeficiency 
Virus, 491
Fungal Meningitis, 491
Tuberculous Meningitis, 491
Primary Amebic 
Meningoencephalitis, 492
SYNOVIAL FLUID, 492
Specimen Collection, 492
Recommended Tests, 492
Gross Examination, 493
Microscopic Examination, 493
Total Cell Count, 493
Differential Leukocyte Count, 493
Crystal Examination, 494
Chemical Analysis, 495
Mucin Clot Test, 495
Glucose, 495
Protein, 495
Enzymes, 495
Organic Acids, 495
Uric Acid, 496
Lipids, 496
Immunologic Studies, 496
Microbiological Examination, 496
PLEURAL FLUID, 496
Specimen Collection, 496
Transudates and Exudates, 496
Recommended Tests, 496
Gross Examination, 497
Microscopic Examination, 498
Cell Counts, 498
Differential Leukocyte Count and 
Cytology, 498
Chemical Analysis, 499
Protein, 499
Glucose, 499
Lactate, 499
Enzymes, 499
Interferon-γ, 499
pH, 499
Lipids, 499
C-Reactive Protein, 500
Tuberculostearic Acid 
(10-Methyloctadecanoic 
Acid), 500
Tumor Markers, 500
Immunologic Studies, 500
Microbiological Examination, 500
PERICARDIAL FLUID, 500
Specimen Collection, 501
Gross Examination, 501
Exudates and Transudates, 501
Microscopic Examination, 501
Chemical Analysis, 501
Protein, 501
Glucose, 501
pH, 501
Lipids, 501
Enzymes, 501
Interferon-γ, 501
Polymerase Chain Reaction, 501
Immunologic Studies, 501
Microbiological Examination, 502
PERITONEAL FLUID, 502
Transudates and Exudates, 502
Specimen Collection, 502
Paracentesis, 502
Diagnostic Peritoneal 
Lavage, 502
Peritoneal Dialysis, 502
Peritoneal Washings, 503
Recommended Tests, 503
Gross Examination, 503
Microscopic Examination, 503
Chemical Analysis, 503
Protein, 503
Glucose, 504
Enzymes, 504
Fibronectin, 504
Lactate, 504
Creatinine and Urea, 504
Bilirubin, 504
pH, 504
Cholesterol, 504
Interleukin-8, 504
Tuberculostearic Acid 
(10-Methyloctadecanoic 
Acid), 504
Tumor Markers, 505
Microbiological Examination, 505
ALTERNATIVE SPECIMENS, 505
Saliva, 505
Hair and Nails, 505
Tissue Aspirates, 505
Billing for Tests in Nonstandard 
Specimens, 505
CHEMICAL MEASUREMENTS IN 
BODY FLUIDS, 506
SELECTED REFERENCES, 506
KEY POINTS
 •  Determining the etiologic cause of fluid accumulation in various body 
cavities (i.e., joints, chest, abdomen) is critical for proper treatment of 
these disorders.
 •  Appropriate laboratory examination of these fluids is therefore critical 
for the diagnosis of numerous diseases (i.e., bacterial, viral and fungal 
infections; distinction between various arthritides; primary [i.e., 
mesothelioma] and metastatic malignancies; among others).
 •  Accurate test interpretation depends on appropriate specimen 
collection, turnaround time, physician/laboratory communication, 
and reliable reference values.
Cerebrospinal Fluid
In adults, approximately 500 mL of cerebrospinal fluid (CSF) is produced 
each day (0.3–0.4 mL/min). The total adult volume varies from 
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parameters vary at different sites. The necessity for a simultaneous serum 
glucose should also be considered. This is best obtained 2–4 hours before 
lumbar puncture because of the delay in serum–CSF equilibrium.
The CSF specimen is usually divided into three serially collected sterile 
tubes: Tube 1 for chemistry and immunology studies; tube 2 for micro­
biological examination; and tube 3 for cell count and differential. An 
additional tube may be inserted in the No. 3 position for cytology if 
a malignancy is suspected. However, under certain conditions, some 
variations are critical. For example, if tube 1 is hemorrhagic because of a 
traumatic puncture, it should not be used when protein studies are the 
most important aspect of the analysis (i.e., suspected multiple sclerosis). 
Indeed, tube 3 should be examined for the major purpose of CSF collec­
tion. Perhaps the only definite statement one can make is that tube 1 
should never be used for microbiology because it may be contaminated 
with skin bacteria. If questions arise, communication between the labora­
tory and the clinician before CSF analysis is critical.
Glass tubes should be avoided because cell adhesion to glass affects the 
cell count and differential. Specimens should be delivered to the laboratory 
and processed quickly to minimize cellular degradation, which begins 
within 1 hour of collection. Refrigeration is contraindicated for culture 
specimens because fastidious organisms (e.g., Haemophilus influenza, Neis-
seria meningitidis) will not survive.
INDICATIONS AND RECOMMENDED TESTS
Indications for lumbar puncture can be divided into four major disease 
categories: meningeal infection, subarachnoid hemorrhage, primary or 
metastatic malignancy, and demyelinating diseases (American College of 
Physicians, 1986). Identification of infectious meningitis, particularly bac­
terial, is the most important indication for CSF examination (Table 29­1). 
Recommended laboratory tests are directed toward identification of these 
disorders (Table 29­2). CSF examination for other diseases is generally less 
helpful but often provides supportive evidence of a clinical diagnosis or 
helps to rule out other diseases (Irani, 2009). Limited routine studies fol­
lowed by reflexive ordering of more focused tests (as needed) on the stored 
specimen have been advocated as a way of improving test efficiency 
(Albright, 1988).
GROSS EXAMINATION
Normal CSF is crystal clear and colorless and has a viscosity similar to that 
of water. Abnormal CSF may appear cloudy, frankly purulent, or pigment 
tinged. Turbidity or cloudiness begins to appear with leukocyte (white 
blood cell [WBC]) counts over 200 cells/µL or red blood cell (RBC) counts 
of 400/µL. However, grossly bloody fluids have RBC counts greater than 
6000/µL. Microorganisms (bacteria, fungi, amebas), radiographic contrast 
material, aspirated epidural fat, and a protein level greater than 150 mg/
dL (1.5 g/L) may also produce varying degrees of cloudiness. Experienced 
observers may be able to detect cell counts of less than 50 cells/µL with 
the unaided eye by observing for Tyndall’s effect (Simon, 1978). Here, 
90–150 mL, about 25 mL of which is in the ventricles and the remainder 
in the subarachnoid space. In neonates, the volume varies from 10–60 mL. 
Thus, the total CSF volume is replaced every 5–7 hours (Wood, 1980). An 
estimated 70% of CSF is derived by ultrafiltration and secretion through 
the choroid plexuses. The ventricular ependymal lining and the cerebral 
subarachnoid space account for the remainder. CSF leaves the ventricular 
system through the medial and lateral foramina, flowing over the brain 
and spinal cord surfaces within the subarachnoid space. CSF resorption 
occurs at the arachnoid villi, predominantly along the superior sagittal 
sinus.
The CSF has several major functions: (1) It provides physical support 
because the 1500­g brain weighs about 50 g when suspended in CSF; (2)it confers a protective effect against sudden changes in acute venous (respi­
ratory and postural) and arterial blood pressure or impact pressure; (3) it 
provides an excretory waste function because the brain has no lymphatic 
system; (4) it is the pathway whereby hypothalamus releasing factors are 
transported to the cells of the median eminence; and (5) it maintains 
central nervous system ionic homeostasis.
The concept of the blood­brain barrier (BBB) is derived from dye­
exclusion (tryphan blue) studies. It consists of two morphologically distinct 
components: A unique capillary endothelium held together by intercellular 
tight junctions; and the choroid plexus, where a single layer of specialized 
choroidal ependymal cells connected by tight junctions overlies fenestrated 
capillaries. The CSF ionic components (e.g., H+, K+, Ca++, Mg++, bicarbon­
ate) are tightly regulated by specific transport systems, whereas glucose, 
urea, and creatinine diffuse freely but require 2 or more hours to equili­
brate. Proteins cross by passive diffusion at a rate dependent on the 
plasma­to­CSF concentration gradient and inversely proportional to their 
molecular weight and hydrodynamic volume (Fishman, 1992). Thus, the 
BBB maintains the relative homeostasis of the central nervous system 
environment during acute perturbations of plasma components.
SPECIMEN COLLECTION AND OPENING 
PRESSURE
Cerebrospinal fluid may be obtained by lumbar, cisternal, or lateral cervical 
puncture or through ventricular cannulas or shunts. Details of the perfor­
mance of lumbar puncture are described elsewhere (Herndon, 1989; Ward, 
1992). Respiratory compromise may occur in infants if the head is flexed 
(Ward, 1992).
A manometer should be attached before fluid removal to record the 
opening pressure. CSF pressure varies with postural changes, blood pres­
sure, venous return, Valsalva maneuvers, and factors that alter cerebral 
blood flow. The normal opening adult pressure is 90–180 mm of water in 
the lateral decubitus position with the legs and neck in a neutral position. 
It may be slightly higher if the patient is sitting up and varies up to 10 mm 
with respiration. However, the pressure may be as high as 250 mm of water 
in obese patients. In infants and young children, the normal range is 10–
100 mm of water, with the adult range attained by age 6–8 years (Fishman, 
1992). Opening pressures above 250 mm H2O are diagnostic of intracra­
nial hypertension, which may be due to meningitis, intracranial hemor­
rhage, and tumors (Seehusen, 2003). If the opening pressure is greater than 
200 mm H2O in a relaxed patient, no more than 2.0 mL should be 
withdrawn.
Idiopathic intracranial hypertension is most commonly seen in obese 
women during their childbearing years. When an elevated opening pres­
sure is noted, CSF must be removed slowly and the pressure carefully 
monitored. Additional CSF should not be removed if the pressure reaches 
50% of the opening pressure (Conly, 1983).
Elevated pressures may be present in patients who are tense or straining 
and in those with congestive heart failure, meningitis, superior vena cava 
syndrome, thrombosis of the venous sinuses, cerebral edema, mass lesions, 
hypoosmolality, or conditions inhibiting CSF absorption. Opening pres­
sure elevation may be the only abnormality in cryptococcal meningitis and 
pseudotumor cerebri (Hayward, 1987). Decreased CSF pressure may be 
present in spinal­subarachnoid block, dehydration, circulatory collapse, 
and CSF leakage. A significant pressure drop after removal of 1–2 mL 
suggests herniation or spinal block above the puncture site, and no further 
fluid should be withdrawn.
Up to 20 mL of CSF may normally be removed. However, the clinician 
not only should be aware of the quantity of CSF required for the requested 
tests to ensure that a sufficient sample is submitted, but should also provide 
an appropriate clinical history to the laboratory. The sample site (i.e., 
lumbar, cisternal, etc.) should be noted because cytologic and chemical 
From  American  College  of  Physicians,  Health  and  Public  Policy  Committee:  
The diagnostic spinal tap. Ann Intern Med 1986;104:880, with permission.
TABLE 29-1 
Diseases Detected by Laboratory Examination of CSF
High sensitivity, high specificity*
Bacterial, tuberculous, and fungal meningitis
High sensitivity, moderate specificity
Viral meningitis
Subarachnoid hemorrhage
Multiple sclerosis
Central nervous system syphilis
Infectious polyneuritis
Paraspinal abscess
Moderate sensitivity, high specificity
Meningeal malignancy
Moderate sensitivity, moderate specificity
Intracranial hemorrhage
Viral encephalitis
Subdural hematoma
*Sensitivity is the ability of a test to detect disease when it is present; specificity is 
the ability of a test to exclude disease when it is not present.
CSF, Cerebrospinal fluid.
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direct sunlight directed on the tube at a 90­degree angle from the observer 
will impart a “sparkling” or “snowy” appearance as suspended particles 
scatter the light.
Clot formation may be present in patients with traumatic taps, com­
plete spinal block (Froin’s syndrome), or suppurative or tuberculous men­
ingitis. It is not seen in patients with subarachnoid hemorrhage. Fine 
surface pellicles may be observed after refrigeration for 12–24 hours. Clots 
may interfere with cell count accuracy by entrapping inflammatory cells.
Viscous CSF may be encountered in patients with metastatic mucin­
producing adenocarcinomas, cryptococcal meningitis due to capsular poly­
saccharide, or liquid nucleus pulposus resulting from needle injury to the 
annulus fibrosus.
Pink-red CSF usually indicates the presence of blood and is grossly 
bloody when the RBC count exceeds 6000/µL. It may originate from a 
subarachnoid hemorrhage, intracerebral hemorrhage, or cerebral infarct, 
or from a traumatic spinal tap.
Xanthochromia
Xanthochromia commonly refers to a pale pink to yellow color in the 
supernatant of centrifuged CSF, although other colors may be present 
(Table 29­3). To detect xanthochromia, the CSF should be centrifuged and 
the supernatant fluid compared with a tube of distilled water. Xanthochro­
mic CSF is pink, orange, or yellow owing to RBC lysis and hemoglobin 
breakdown. Pale pink to orange xanthochromia from released oxyhemo­
globin is usually detected by lumbar puncture performed 2–4 hours after 
the onset of subarachnoid hemorrhage, although it may take as long as 12 
hours. Peak intensity occurs in about 24–36 hours and then gradually 
disappears over the next 4–8 days. Yellow xanthochromia is derived from 
bilirubin. It develops about 12 hours after a subarachnoid bleed and peaks 
at 2–4 days, but may persist for 2–4 weeks.
Visible CSF xanthochromia may also be due to the following: (1) oxy­
hemoglobin resulting from artifactual red cell lysis caused by detergent 
contamination of the needle or collecting tube, or a delay of longer than 
1 hour without refrigeration before examination; (2) bilirubin (bilirhachia) 
in jaundiced patients; (3) CSF protein levels over 150 mg/dL, which are 
also present in bloody traumatic taps (>100,000 RBCs/µL) or in pathologic 
states such as complete spinal block, polyneuritis, and meningitis; (4) 
merthiolate disinfectant contamination; (5) carotenoids (orange) in people 
with dietary hypercarotenemia (i.e., hypervitaminosis A); (6) melanin 
(brownish) from meningeal metastatic melanoma; and (7) rifampin therapy 
(red­orange).
Although spectral absorbance scans provide an objective record of 
xanthochromia, careful gross CSF inspection has comparable sensitivity 
(Britton, 1983). Spectrophotometrycan also help to differentiate 
hemoglobin­derived substances from other xanthochromic pigments with 
different maximal absorption peaks.
Modified  from  Kjeldsberg  CR,  Knight  JA.  Body  fluids:  laboratory  examination  
of amniotic, cerebrospinal, seminal, serous, and synovial fluids. 3rd ed. Chicago:
© American Society for Clinical Pathology; 1993, with permission.
TABLE 29-2 
Recommended CSF Laboratory Tests
Routine
Opening CSF pressure
Total cell count (WBC and RBC)
Differential cell count (stained smear)
Glucose (CSF/plasma ratio)
Total protein
Useful under certain conditions
Cultures (bacteria, fungi, viruses, Mycobacterium tuberculosis)
Gram stain, acid-fast stain
Fungal and bacterial antigens
Enzymes (LD, ADA, CK-BB)
Lactate
Polymerase chain reaction (TB, viruses)
Cytology
Electrophoresis (protein, immunofixation)
Proteins (C-reactive, 14-3-3, τ, β-amyloid, transferrin)
VDRL test for syphilis
Fibrin-derivative D-dimer
Tuberculostearic acid
ADA,  Adenosine  deaminase;  CK-BB,  creatine  kinase-BB;  CSF,  cerebrospinal  fluid; 
LD, lactate dehydrogenase; RBC, red blood cell; TB, tuberculosis; VDRL, Venereal 
Disease Research Laboratories; WBC, white blood cell.
TABLE 29-3 
Xanthochromia and Associated Diseases/Disorders
CSF supernatant color Associated diseases/disorders
Pink RBC lysis/hemoglobin breakdown products
Yellow RBC lysis/hemoglobin breakdown products
Hyperbilirubinemia
CSF protein >150 mg/dL (1.5 g/L)
Orange RBC lysis/hemoglobin breakdown products
Hypervitaminosis A (carotenoids)
Yellow-green Hyperbilirubinemia (biliverdin)
Brown Meningeal metastatic melanoma
CSF, Cerebrospinal fluid; RBC, red blood cell.
Differential Diagnosis of Bloody CSF
A traumatic tap occurs in about 20% of lumbar punctures. Distinction of 
a traumatic puncture from a pathologic hemorrhage is, therefore, of vital 
importance. Although the presence of crenated RBCs is not useful, the 
following observations may be helpful in distinguishing the two forms of 
bleeding.
1. In a traumatic tap, the hemorrhagic fluid usually clears between the 
first and third collected tubes but remains relatively uniform in 
subarachnoid hemorrhage.
2. Xanthochromia, microscopic evidence of erythrophagocytosis, or 
hemosiderin­laden macrophages indicate a subarachnoid bleed in 
the absence of a prior traumatic tap. RBC lysis begins as early as 
1–2 hours after a traumatic tap. Thus, rapid evaluation is necessary 
to avoid false­positive results.
3. A commercially available latex agglutination immunoassay test 
for cross­linked fibrin derivative d­dimer is specific for fibrin deg­
radation and is negative in traumatic taps (Lang, 1990). However, 
false­positive results might be expected in disseminated intra­
vascular coagulation, fibrinolysis, or trauma from repeated lumbar 
punctures.
MICROSCOPIC EXAMINATION
Total Cell Count
Although the traditional manual method for cell counting in CSF samples, 
using undiluted CSF in a manual counting chamber, continues to be a 
useful approach, because of the low cell counts frequently encountered in 
CSF, the precision of manual counting in these samples is inherently 
limited (Barnes, 2004). For example, using 18 large squares (1 mm2 each) 
in a Fuchs­Rosenthal–type chamber with a depth of 0.2 mm, a total 
volume of 3.6 µL (18 × 0.2 µL/square) is examined. With 5 cells/µL, 
a total of 18 cells is counted. The coefficient of variation (CV), defined as 
100 divided by the square root of the number of cells counted, is 24%; ±2 
CV is about 48%. A Neubauer hemocytometer with nine 1­mm2 squares 
with a depth of 0.1 mm has a CV of 45% (+90% for 2 CV) with the same 
cell concentration. Improvements in the hardware and software in flow 
cytometers now allow reliable use of these instruments in performing 
automated total WBC counts and WBC differential counts (Hoffman, 
2002; Aune, 2004), and even in detecting bacteria (Nanos, 2008) in CSF 
samples; however, the low clinical decision levels for total WBC count and 
enumeration of some WBC types in CSF and limitations in detecting small 
numbers of RBCs continue to represent challenges in the use of these 
instruments with CSF (Hoffman, 2002; Andrews, 2005; Glasser, 2009; 
Kleine, 2009). Because of these limitations, laboratories should exercise 
caution in utilizing automated cell counters with CSF samples and should 
carefully follow manufacturer and Clinical and Laboratory Standards Insti­
tute guidelines (CLSI Approved Guideline H56­A, 2006) when imple­
menting these automated methods.
The normal leukocyte cell count in adults is 0–5 cells/µL. It is higher 
in neonates, ranging from 0–30 cells/µL, with the upper limit of normal 
decreasing to adult values by adolescence. No RBCs should be present in 
normal CSF. If numerous (except a traumatic tap), a pathologic process is 
probable (e.g., trauma, malignancy, infarct, hemorrhage). Although red 
cell counts have limited diagnostic value, they may give a useful approxi­
mation of the true CSF WBC or total protein in the presence of a trau­
matic puncture by correcting for leukocytes or protein introduced by the 
traumatic puncture. To be valid, all measurements (WBC, RBC, protein) 
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must be performed on the same tube. This procedure also assumes that 
the blood is derived exclusively from the traumatic tap. The corrected 
WBC count is as follows:
WBC WBC WBCcorr obs added= −
where
WBC WBC RBC RBCadded BLD CSF BLD= ×
and
WBCobs = CSF leukocyte count
WBCadded = leukocytes added to CSF by traumatic tap
WBCBLD = peripheral blood leukocyte count
RBCCSF = CSF erythrocyte count
RBCBLD = peripheral blood erythrocyte count.
An analogous formula may be used to correct for added total protein 
(TP):
TP TP HCT RBC RBCadded serum CSF BLD= × −( )[ ] ×1
In the presence of a normal peripheral blood RBC count and serum 
protein, these corrections amount to about 1 WBC for every 700 RBCs 
and 8 mg/dL protein for every 10,000 RBCs/µL. This latter RBC correc­
tion factor is reasonably accurate as long as the peripheral WBC count is 
not extremely high or low. Moreover, the accuracy of these corrections is 
limited by the precision of the CSF RBC count, which can significantly 
limit its value.
An observed/expected (added) WBC count ratio greater than 10 has a 
sensitivity of 88% and a specificity of 90% for bacterial meningitis. When 
the predicted WBC is below the observed count, the probability of bacte­
rial meningitis appears to be low (Mayefsky, 1987; Bonadio, 1990).
Differential Cell Count
Suggested differential count reference ranges are presented in Table 29­4. 
A differential performed in a counting chamber is unsatisfactory because 
the low cell numbers give rise to poor precision, and identifying the cell 
type beyond granulocytes and “mononuclears” is difficult in a wet prepara­
tion. Direct smears of the centrifuged CSF sediment are also subject to 
significant error from cellular distortion and fragmentation.
The cytocentrifuge method is rapid, requires minimal training, and 
allows Wright’s staining of air­dried cytospins. Indeed, it is the recom­
mended method for differential cell counts in all body fluids (Rabinovitch, 
1994). Cell yield and preservation are better than with simple centrifuga­
tion. From 30–50 cells can be concentrated from 0.5 mL of “normal” CSF. 
Variable artifactual distortions may be seen, but they are minimized when 
the specimen is fresh, albumin is added to the specimen (2 drops of 22% 
bovine serum albumin), and the cell concentration is adjusted to about 
300 WBCs/L prior to centrifugation (Kjeldsberg, 1993). Manual differen­
tial cell counting on a cytocentrifuge preparation of CSF continues to be 
the most reliable method, even with low cell numbers. Although auto­
mated differential counts may be safely performed on CSF samples using 
flowcytometers (Hoffman, 2002; Aulesa, 2003), confirmation of the auto­
mated differential count by manual examination of a cytocentrifuged smear 
is recommended with some instruments (Aune, 2004) and is a requirement 
with specimens at risk of containing neoplastic cells.
Filtration and sedimentation methods are too cumbersome for routine 
use. Filtration does, however, allow concentration of large volumes of CSF 
for cytologic examination or culture, while retaining the fluid filtrate for 
additional studies.
In adults, normal CSF contains small numbers of lymphocytes and 
monocytes in an approximate 70 : 30 ratio (Fig. 29­1). A higher proportion 
of monocytes is present in young children, in whom up to 80% may be 
Figure 29-1  Cerebrospinal fluid cytology (lymphocyte to monocyte distribution 
ratio 70:30). 
Figure 29-2  Choroid plexus cells in cerebrospinal fluid. 
Figure 29-3  Cluster  of  blast-like  cells  in  cerebrospinal  fluid  from  premature 
newborn. (From Kjeldsberg CR, Knight JA. Body fluids: laboratory examination of amni-
otic, cerebrospinal, seminal, serous and synovial fluids. 3rd ed. Chicago: © American 
Society for Clinical Pathology; 1993, with permission.)
TABLE 29-4 
CSF Reference Values for Differential Cytocentrifuge Counts
Cell type Adults, % Neonates, %
Lymphocytes 62 ± 34 20 ± 18
Monocytes 36 ± 20 72 ± 22
Neutrophils 2 ± 5 3 ± 5
Histiocytes Rare 5 ± 4
Ependymal cells Rare Rare
Eosinophils Rare Rare
CSF, Cerebrospinal fluid.
normal (Pappu, 1982). Erythrocytes due to minor traumatic bleeding are 
commonly seen, especially in infants. Small numbers of neutrophils 
(PMNs) may also be seen in “normal” CSF specimens, most likely as a 
result of minor hemorrhage (Hayward, 1988) and improved cell concentra­
tion methods. No general consensus regarding an upper limit of normal 
for PMNs has been established. We accept up to 7% neutrophils with a 
normal WBC count. Over 60% neutrophils has been reported in high­risk 
neonates without meningitis (Rodriguez, 1990). The number of PMNs 
may be decreased by as much as 68% within the first 2 hours after lumbar 
puncture owing to cell lysis (Steele, 1986).
Traumatic puncture may result in the presence of bone marrow cells, 
cartilage cells, squamous cells, ganglion cells, and soft tissue elements. In 
addition, ependymal and choroid plexus cells may rarely be seen (Fig. 
29­2). Moreover, blast­like primitive cell clusters, most likely of germinal 
matrix origin, are sometimes found in premature infants with intraven­
tricular hemorrhage (Fig. 29­3).
Increased CSF neutrophils occur in numerous conditions (Table 
29­5). In early bacterial meningitis, the proportion of PMNs usually 
exceeds 60%. However, in about one quarter of cases of early viral men­
ingitis, the proportion of PMNs also exceeds 60%. Viral­induced neutro­
philia usually changes to a lymphocytic pleocytosis within 2–3 days. A total 
PMN count of over 1180 cells/µL (or more than 2000 WBCs/µL) has a 
99% predictive value for bacterial meningitis (Spanos, 1989). Persistent 
neutrophilic meningitis (over 1 week) may be noninfectious or due to less 
common pathogens such as Nocardia, Actinomyces, Aspergillus, and the zygo­
mycetes (Peacock, 1984).
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Increased CSF lymphocytes have been reported in various diseases/
disorders (Table 29­6). Lymphocytosis (>50%) may occur in early acute 
bacterial meningitis when the CSF leukocyte count is under 1000/µL 
(Powers, 1985). Reactive lymphoplasmacytoid and immunoblastic variants 
may be present, particularly with viral meningoencephalitis. Blast­like 
lymphocytes may be seen admixed with small and large lymphocytes in the 
CSF of neonates.
Plasma cells, not normally present in CSF, may appear in a variety of 
inflammatory and infectious conditions (Table 29­7), along with large and 
small lymphocytes, and in association with malignant brain tumors 
TABLE 29-5 
Causes of Increased CSF Neutrophils
Meningitis
Bacterial meningitis
Early viral meningoencephalitis
Early tuberculous meningitis
Early mycotic meningitis
Amebic encephalomyelitis
Other infections
Cerebral abscess
Subdural empyema
AIDS-related CMV radiculopathy
Following seizures
Following CNS hemorrhage
Subarachnoid
Intracerebral
Following CNS infarct
Reaction to repeated lumbar punctures
Injection of foreign material in subarachnoid space (e.g., methotrexate, 
contrast media)
Metastatic tumor in contact with CSF
AIDS, Acquired  immunodeficiency  syndrome; CMV,  cytomegalovirus; CNS,  central 
nervous system; CSF, cerebrospinal fluid.
TABLE 29-6 
Causes of CSF Lymphocytosis
Meningitis
Viral meningitis
Tuberculous meningitis
Fungal meningitis
Syphilitic meningoencephalitis
Leptospiral meningitis
Bacterial due to uncommon organisms
Early bacterial meningitis where leukocyte counts are relatively low
Parasitic infestations (e.g., cysticercosis, trichinosis, toxoplasmosis)
Aseptic meningitis due to septic focus adjacent to meninges
Degenerative disorders
Subacute sclerosing panencephalitis
Multiple sclerosis
Drug abuse encephalopathy
Guillain-Barré syndrome
Acute disseminated encephalomyelitis
Other inflammatory disorders
Handl syndrome (headache with neurologic deficits and CSF 
lymphocytosis)
Sarcoidosis
Polyneuritis
CNS periarteritis
CNS, Central nervous system; CSF, cerebrospinal fluid.
Modified with  permission  from Kjeldsberg CR,  Knight  JA.  Body  fluids:  laboratory 
examination of amniotic, cerebrospinal, seminal, serous and synovial fluids. 3rd 
ed. Chicago: © American Society for Clinical Pathology; 1993.
TABLE 29-8 
Causes of CSF Eosinophilic Pleocytosis
Commonly associated with
Acute polyneuritis
CNS reaction to foreign material 
(drugs, shunts)
Fungal infections
Idiopathic eosinophilic meningitis
Idiopathic hypereosinophilic 
syndrome
Parasitic infections
Infrequently associated with
Bacterial meningitis
Leukemia/lymphoma
Myeloproliferative disorders
Neurosarcoidosis
Primary brain tumors
Tuberculous meningoencephalitis
Viral meningitis
CNS, Central nervous system; CSF, cerebrospinal fluid.
TABLE 29-7 
Inflammatory and Infectious Causes of CSF Plasmacytosis
•  Acute viral infections
•  Guillain-Barré syndrome
•  Multiple sclerosis
•  Parasitic CNS infestations
•  Sarcoidosis
•  Subacute sclerosing panencephalitis
•  Syphilitic meningoencephalitis
•  Tuberculous meningitis
CNS, Central nervous system; CSF, cerebrospinal fluid.
Figure 29-4  Eosinophils  in cerebrospinal fluid from a child with malfunctioning 
ventricular shunt. 
(Fishman, 1992). Multiple myeloma may also rarely involve the meninges 
(Oda, 1991).
Although eosinophils are rarely present in normal CSF, they may be 
increased in a variety of central nervous system (CNS) conditions (Table 
29­8). For example, eosinophilia is frequently mild (1%–4%) in a general 
inflammatory response, but in children with malfunctioning ventricular 
shunts, it may be marked (Fig. 29­4). A suggested criterion for eosinophilic 
meningitis is 10% eosinophils (Kuberski, 1981); parasitic invasion of the 
CNS is the most common cause worldwide. Coccidioides immitis is a signifi­
cant cause of CSF eosinophilia in endemic regions of the United States 
(Ragland, 1993).
Increased CSF monocytes lack diagnostic specificity and are usually 
part of a “mixed cell reaction” that includes neutrophils, lymphocytes, and 
plasma cells. This pattern is seen in tuberculous and fungal meningitis, 
chronic bacterial meningitis (i.e., Listeria monocytogenes and others), lepto­
spiral meningitis, ruptured brain abscess, Toxoplasma meningitis, and 
amebic encephalomeningitis. A mixed cell pattern withoutneutrophils is 
characteristic of viral and syphilitic meningoencephalitis. Macrophages 
with phagocytosed erythrocytes (erythrophages) appear from 12–48 
hours following a subarachnoid hemorrhage or traumatic tap. Hemosiderin­
laden macrophages (siderophages) appear after about 48 hours and may 
persist for weeks (Fig. 29­5). Brownish yellow or red hematoidin crystals 
may form after a few days.
Figure 29-5  Hemosiderin-laden macrophages (siderophages)  from the cerebro-
spinal  fluid  of  a  patient  with  subarachnoid  hemorrhage.  Hemosiderin  crystals 
(golden-yellow) are also present. (From Kjeldsberg CR, Knight JA. Body fluids: labora-
tory examination of amniotic, cerebrospinal, seminal, serous and synovial fluids. 3rd ed. 
Chicago: © American Society for Clinical Pathology; 1993, with permission.)
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are significantly less common (Bigner, 1992; Walts, 1992). T cells predomi­
nate in normal and inflammatory conditions, whereas most lymphomas, 
especially those occurring in immunocompromised hosts, are of B cell 
lineage. Lymphoblastic lymphoma, the most common T cell lymphoma, 
can be detected by terminal deoxynucleotidyl transferase stain.
Multiparameter flow cytometric immunophenotypic studies and/or 
molecular DNA analysis may significantly improve diagnostic sensitivity 
and specificity in CSF samples involved by leukemic or lymphoma cells 
(Rhodes, 1996; Finn, 1998; Scrideli, 2004; Bromberg, 2007; Quijano, 
2009), and these are used increasingly as part of a complete evaluation in 
patients being worked up for these conditions.
Amebae, fungi (especially Cryptococcus neoformans), and Toxoplasma 
gondii organisms may be present on cytocentrifuge specimens but may be 
difficult to recognize without confirmatory stains.
CHEMICAL ANALYSIS
Reference values for lumbar cerebrospinal fluid in adults are listed in 
Table 29­9.
Proteins
Total Protein
More than 80% of the CSF protein content is derived from blood plasma, 
in concentrations of less than 1% of the plasma level (Table 29­10).
Morphologic cerebrospinal fluid examination for tumor cells has mod­
erate sensitivity and high specificity (97%–98%) (Marton, 1986). Sensitiv­
ity depends on the type of neoplasm. CSF examination of leukemic patients 
has the highest sensitivity (about 70%), followed by metastatic carcinoma 
(20%–60%) and primary CNS malignancies (30%). Sensitivity may be 
optimized by using filtration methods with larger fluid volumes or by 
performing serial punctures in patients in whom a neoplasm is strongly 
suspected. Processing of CSF samples using liquid­based thin­layer 
methods also increases sensitivity in the detection of neoplastic cells and 
enhances preservation of these cells for potential immunocytochemical 
analysis (Sioutopoulou, 2008). These liquid­based methods are now com­
monly used for cytopathologic examination of CSF and other body cavity 
fluid specimens.
Leukemic involvement of the meninges is more frequent in patients 
with acute lymphoblastic leukemia (Fig. 29­6) than in those with acute 
myeloid leukemia (Fig. 29­7); both are significantly more common than 
CNS involvement in the chronic leukemias. A leukocyte count over 
5 cells/µL with unequivocal lymphoblasts in cytocentrifuged preparations 
is commonly accepted as evidence of CSF involvement. The incidence 
of CNS relapse in children with lymphoblasts but cell counts lower 
than 6 cells/µL appears to be low and is not significantly different from 
cases in which no blasts are identified (Odom, 1990; Gilchrist, 1994; 
Tubergen, 1994).
Non­Hodgkin lymphomas involving the leptomeninges are usually 
high­grade tumors (lymphoblastic, large cell immunoblastic, and Burkitt’s 
lymphomas) (Fig. 29­8); low­grade lymphomas and Hodgkin lymphoma 
Figure 29-6  Acute lymphoblastic leukemia in cerebrospinal fluid. Note uniformity 
of the blast cells. 
Figure 29-7  Acute myeloid leukemia in cerebrospinal fluid. 
Figure 29-8  Burkitt’s lymphoma in cerebrospinal fluid. The cells are characterized 
by  blue  cytoplasm with  vacuoles  and  slightly  clumped  chromatin  pattern.  (From 
Kjeldsberg CR, Knight JA. Body fluids: laboratory examination of amniotic, cerebrospinal, 
seminal, serous and synovial fluids. 3rd ed. Chicago: © American Society for Clinical 
Pathology; 1993, with permission.)
TABLE 29-9 
Adult Lumbar CSF Reference Values
Analyte Conventional units SI units
Protein 15–45 mg/dL 0.15–0.45 g/L
Prealbumin 2%–7%
Albumin 56%–76%
α1-Globulin 2%–7%
α2-Globulin 4%–12%
β-Globulin 8%–18%
γ-Globulin 3%–12%
Electrolytes
Osmolality 280–300 mOsm/L 280–300 mmol/L
Sodium 135–150 mEq/L 135–150 mmol/L
Potassium 2.6–3.0 mEq/L 2.6–3.0 mmol/L
Chloride 115–130 mEq/L 115–130 mmol/L
Carbon dioxide 20–25 mEq/L 20–25 mmol/L
Calcium 2.0–2.8 mEq/L 1.0–1.4 mmol/L
Magnesium 2.4–3.0 mEq/L 1.2–1.5 mmol/L
Lactate 10–22 mg/dL 1.1–2.4 mmol/L
pH
Lumbar fluid 7.28–7.32
Cisternal fluid 7.32–7.34
pCO2
Lumbar fluid 44–50 mm Hg
Cisternal fluid 40–46 mm Hg
pO2 40–44 mm Hg
Other Constituents
Ammonia 10–35 µg/dL 6–20 µmol/L
Glutamine 5–20 mg/dL 0.3–1.4 mmol/L
Creatinine 0.6–1.2 mg/dL 45–92 µmol/L
Glucose 50–80 mg/dL 2.8–4.4 mmol/L
Iron 1–2 µg/dL 0.2–0.4 µmol/L
Phosphorus 1.2–2.0 mg/dL 0.4–0.7 mmol/L
Total lipid 1–2 mg/dL 0.01–0.02 g/L
Urea 6–16 mg/dL 2.0–5.7 mmol/L
Urate 0.5–3.0 mg/dL 30–180 µmol/L
Zinc 2–6 µg/dL 0.3–0.9 µmol/L
CSF, cerebrospinal fluid; pCO2, partial pressure of carbon dioxide; pO2, partial pres-
sure of oxygen.
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Prealbumin (transthyretin), transferrin, and small quantities of nerve 
tissue–specific proteins are the major qualitative differences that normally 
exist between CSF and plasma proteins. Although some authors have 
argued against routine measurement of total protein (American College of 
Physicians, 1986), it is the most common abnormality found in CSF. Thus, 
an increased CSF protein serves as a useful, albeit nonspecific, indicator 
of meningeal or CNS disease.
Reference Values. CSF total protein reference values vary considerably 
between laboratories owing to differences in methods, instrumentation, 
and type of reference standard used (College of American Pathologists 
CSF Chemistry Survey, Set M­B, 1991*; Gerbaut, 1986). CSF protein 
levels of 15–45 mg/dL have long been accepted as the “normal” reference 
range (Silverman, 1994). Using the classic Lowry method, the reported 
adult range was 24.1–48.5 mg/dL (Tibbling, 1977). Others reported a 
reference range of 14–49 mg/dL using a trichloroacetic acid–Ponceau S 
method (Breebaart, 1978), and of 22.3–50.3 mg/dL with a biuret method 
(Ahonen, 1978). Reference levels were also compared using three different 
methods: (1) A modified biuret technique; (2) a Dupont aca method in 
which protein was precipitated and then reacted with trichloroacetic acid; 
and (3) a Kodak Ektachem colorimetric slide technique (Lott, 1989). All 
three methods gave similar, although significantly higher, levels than those 
previously reported (i.e., 14–62 mg/dL, 16–61 mg/dL, and 12–60 mg/dL, 
respectively).
Although discrepancies in gender and in those over the age of 60 years 
have been reported, the differences are probably not significant. However, 
infants have significantly higher CSF protein levels than older children 
and adults. Thus, mean levels of 90 mg/dL for term infants and 115 mg/
dL for preterm infants were reported; the upper levels were 150 mg/dL 
and 170 mg/dL, respectively (Sarff, 1976). Similarly, others recently noted 
that the CSF protein concentration fell rapidly from birth to 6 months of 
age (mean levels, 108 mg/dL–40 mg/dL), plateaued between 3 and 10 
years (mean, 32 mg/dL), and thenrose slightly from 10–16 years (mean, 
41 mg/dL) (Biou, 2000).
Elevated CSF protein levels may be caused by increased permeability 
of the blood­brain barrier, decreased resorption at the arachnoid villi, 
mechanical obstruction of CSF flow due to spinal block above the puncture 
site, or an increase in intrathecal immunoglobulin (Ig) synthesis. Common 
conditions associated with elevated lumbar CSF protein values (>65 mg/
dL) are summarized in Table 29­11.
Low lumbar CSF total protein levels (<20 mg/dL) normally occur in 
some young children between 6 months and 2 years of age and in patients 
with conditions associated with increased CSF turnover. These include the 
following: (1) Removal of large CSF volumes; (2) CSF leaks induced by 
trauma or lumbar puncture; (3) increased intracranial pressure, probably 
due to an increased rate of protein resorption by the arachnoid villi; and 
(4) hyperthyroidism (Fishman, 1992).
Protein electrophoresis of concentrated normal CSF reveals two dis­
tinct differences from serum: A prominent transthyretin (prealbumin) 
band and two transferrin bands. Transthyretin is relatively high because 
of its dual synthesis by the liver and the choroid plexus. The second trans­
ferrin band, referred to as β2­transferrin, migrates more slowly than its 
Adapted from Felgenhauer K. Klin Wochenschr 1974;52:1158, with permission.
TABLE 29-10 
Mean Concentrations of Plasma and CSF Proteins
Protein CSF, mg/L Plasma/CSF ratio
Prealbumin 17.3 14
Albumin 155.0 236
Transferrin 14.4 142
Ceruloplasmin 1.0 366
Immunoglobulin (Ig)G 12.3 802
IgA 1.3 1346
α2-Microglobulin 2.0 1111
Fibrinogen 0.6 4940
IgM 0.6 1167
β-Lipoprotein 0.6 6213
CSF, Cerebrospinal fluid.
*College of American Pathologists, 325 Waukegan Road, Northfield, Ill.
TABLE 29-11 
Conditions Associated With Increased CSF Total Protein
Traumatic spinal puncture
Increased blood–CSF permeability
Arachnoiditis (e.g., following methotrexate therapy)
Meningitis (bacterial, viral, fungal, tuberculous)
Hemorrhage (subarachnoid, intracerebral)
Endocrine/metabolic disorders
Milk–alkali syndrome with hypercalcemia
Diabetic neuropathy
Hereditary neuropathies and myelopathies
Decreased endocrine function (thyroid, parathyroid)
Other disorders (uremia, dehydration)
Drug toxicity
Ethanol, phenothiazines, phenytoin
CSF circulation defects
Mechanical obstruction (tumor, abscess, herniated disk)
Loculated CSF effusion
Increased immunoglobulin (Ig)G synthesis
Multiple sclerosis
Neurosyphilis
Subacute sclerosing panencephalitis
Increased IgG synthesis and blood–CSF permeability
Guillain-Barré syndrome
Collagen vascular diseases (e.g., lupus, periarteritis)
Chronic inflammatory demyelinating polyradiculopathy
CSF, Cerebrospinal fluid.
serum equivalent owing to cerebral neuraminidase digestion of sialic acid 
residues.
Methods. Turbidimetric methods, commonly based on trichloroacetic 
acid (TCA) or sulfosalicylic acid and sodium sulfate for protein precipita­
tion, are popular because they are simple and rapid, and require no special 
instrumentation. However, they are temperature sensitive and require 
much larger specimen volumes (about 0.5 mL). Moreover, some methods 
are prone to significant variation from changes in the albumin/globulin 
ratio (Schriever, 1965). A false protein elevation may be observed using 
TCA methods in the presence of methotrexate (Kasper, 1988). 
Benzethonium chloride and benzalkonium chloride have been used as 
precipitating agents in automated methods and micromethods (Luxton, 
1989; Shephard, 1992).
Colorimetric methods include the Lowry method, dye­binding, 
methods using Coomassie brilliant blue (CBB) or Ponceau S, and the 
modified Biuret method. The CBB method is rapid and highly sensitive, 
and can be used with small sample sizes. Immunologic methods measure 
specific proteins, require only 25–50 µL of CSF, and are relatively simple 
to perform once conditions and reagents have been standardized. Auto­
mated methods are also commonly used and usually show good correlation 
with standard methods (Lott, 1989).
Albumin and IgG Measurements
The permeability of the blood­brain barrier may be assessed by immuno­
chemical quantification of the CSF albumin/serum albumin ratio in grams 
per deciliter (g/dL). The normal ratio of 1 : 230 (Tourtellotte, 1985) yields 
an unwieldy decimal of 0.004, which prompted the use of the CSF/serum 
albumin index, which is arbitrarily calculated as follows:
CSF Serum albumin index
CSF albumin mg dL
Serum albumin g dL
=
( )
( ) (29-1)
An index value less than 9 is consistent with an intact barrier. Slight 
impairment is considered with index values of 9–14, moderate impairment 
with values of 14–30, and severe impairment with values greater than 
30 (Silverman, 1994). The index is slightly elevated in infants up to 
6 months of age, reflecting the immaturity of the blood­brain barrier, 
and increases gradually after age 40 years. A traumatic tap invalidates the 
index calculation.
Increased intrathecal IgG synthesis is reflected by an increase in the 
CSF/serum IgG ratio:
CSF Serum IgG ratio
CSF IgG mg dL
Serum IgG g dL
=
( )
( ) (29-2)
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High-resolution agarose gel electrophoresis of concentrated CSF 
from patients with MS often shows discrete populations of IgG, the 
oligoclonal bands. Although these discrete IgG populations are normally 
absent, two or more bands are necessary to support the diagnosis of MS; 
a single band is not considered a positive result. Using this technique, 
oligoclonal bands have been reported in 83%–94% of patients with defi­
nite MS, 40%–60% of those with probable MS, and 20%–30% of possible 
MS cases. However, they are also frequently present in patients with 
subacute sclerosing panencephalitis, various viral CNS infections, neuro­
syphilis, neuroborreliosis, cryptococcal meningitis, Guillain­Barré syn­
drome, transverse myelitis, meningeal carcinomatosis, glioblastoma 
multiforme, Burkitt’s lymphoma, chronic relapsing polyneuropathy, 
Behçet’s disease, cysticercosis, and trypanosomiasis, among others (Trotter, 
1989; Chalmers, 1990; Fishman 1992; Hall, 1992). Subsequent studies 
indicate that agarose gel electrophoresis sensitivity for MS is less than 
previously reported (see later).
Oligoclonal light chains (both κ and λ) are present in about 90% 
of MS patients (Gallo, 1989; Sindie, 1991). They have also occasionally 
been identified in the CSF of those who are negative for IgG oligoclonal 
bands. However, because of their uncommon occurrence in the absence 
of IgG and cost­ineffectiveness, as well as the ready availability of 
magnetic resonance imaging, it is unlikely that this technique will become 
common.
Coomassie brilliant blue or paragon violet stains can resolve 
oligoclonal bands in only 5 µg of IgG (Silverman, 1994). However, silver 
staining is 20–50 times more sensitive than CBB and can be used on 
unconcentrated CSF. It is important to note that these electrophoretic 
techniques must be simultaneously carried out on the patient’s serum to 
be certain that a polyclonal gammopathy is not present (e.g., liver disease, 
systemic lupus, rheumatoid arthritis, chronic granulomatous disease) 
because these disorders may be accompanied by Ig diffusion into the CSF, 
yielding false­positive results.
Immunofixation electrophoresis (IFE) is more sensitive than agarose 
gel electrophoresis and does not require CSF concentration (Cawley, 
1976). A subsequent study reported a sensitivity of 74% using this tech­
nique compared with 57% for agarose gel electrophoresis (Cavuoti, 1998). 
More recently, using a semiautomated immunofixation­peroxidase tech­
nique, the sensitivity was 83% and the specificity was 79% in patients with 
clinically definite MS (Richard, 2002). However, IFE provides fewer bandsthan isoelectric focusing and IgG immunoblotting (IgG­IEF). More­
over, the bands obtained by IFE tend to be more diffuse.
IgG­IEF performed on paired CSF and serum samples is the most 
sensitive method for the detection of oligoclonal bands (Andersson, 1994). 
One study showed that IgG­IEF detected 100% of definite MS, but only 
about 50% were positive by agarose electrophoresis (Lunding, 2000). 
Others detected 91% of MS cases but only 68% with agarose (Seres, 1998). 
Similarly, a semiautomated IgG­IEF technique identified 90% of MS cases 
compared with 60% for agarose electrophoresis (Fortini, 2003). In 2005, 
an international consensus standard for the diagnosis of MS established 
IgG­IEF as the method of choice for qualitative detection of oligoclonal 
IgG bands as evidence of intrathecal synthesis of IgG (Freedman, 2005). 
This method is more sensitive and specific than quantitative methods.
In summary, the diagnosis of MS, as with many other neurologic dis­
orders, is ultimately a clinical one based on neurologic history and physical 
examination. Nevertheless, advanced laboratory results in CSF, such as 
elevated IgG indices and particularly the detection of oligoclonal IgG 
bands, as well as neuroimaging techniques, have proved invaluable in the 
diagnosis of MS.
Other CSF Proteins
Approximately 300 different proteins have been identified in CSF using 
two­dimensional electrophoresis, the first dimension being isoelectric 
focusing and the second polyacrylamide gel in the presence of sodium 
dodecyl sulfate (Harrington, 1986). Using this technique, four abnormal 
proteins were identified in patients with Creutzfeldt­Jakob disease (CJD). 
Two of these proteins (molecular mass about 40 kilodaltons [kDa] each) 
were present in some, but not all, patients with herpes simplex encephalitis, 
Parkinson’s disease, Guillain­Barré syndrome, and schizophrenia. They 
were not present in various other neurologic disorders, nor in 100 normal 
CSF control specimens. However, these and two other proteins (molecular 
masses about 26 and 29 kDa) were present in all cases of CJD and in 5 of 
10 cases of herpes simplex encephalitis. Neither of these latter proteins 
was present in any other neurologic disease or in controls.
Increased concentrations of various specific CSF proteins have been 
associated with several CNS diseases (Table 29­12).
The normal ratio is 1/390 or 0.003 (Tourtellotte, 1985). Similar to the 
albumin index, the CSF/serum IgG index may be obtained by using mil­
ligrams per deciliter for the CSF IgG value. The CSF/serum IgG index 
normal range is 3.0–8.7.
The CSF/serum IgG index can be elevated by intrathecal IgG syn­
thesis or increased plasma IgG crossover from breakdown of the blood­
brain barrier. Ig derived from plasma crossover may be corrected by 
dividing the CSF/serum IgG index by the CSF/albumin index to yield the 
CSF IgG index.
CSF IgG index
CSF IgG mg dL Serum IgG g dL
CSF albumin mg dL Serum
=
( ) ( )
( ) aalbumin g dL( )
(29-3)
or
CSF IgG index
CSF IgG mg dL Serum albumin g dL
Serum IgG g dL CS
=
( ) × ( )
( ) × FF albumin mg dL( ) (29-4)
The normal reference range for the IgG index varies, reflecting varia­
tions in determination of the four index components. A reasonable normal 
upper limit is 0.8 (Souverijn, 1989). However, each laboratory should 
determine its own critical ratio.
The IgG synthesis rate is calculated by an empirical formula 
(Tourtellotte, 1985):
IgG synthesis rate mg day CSF IgG Serum IgG
CSF albumin S
( ) = −( ) −[
−
369
eerum albumin
Serum IgG Serum albumin dL day
230
0 43 5
( ) ×
( ) × × ].
 
(29-5)
All protein concentrations are expressed in milligrams per deciliter. 
The first bracketed term represents the difference between measured CSF 
IgG and the IgG expected from diffusion across a normal blood­brain 
barrier; 369 is the normal serum/CSF ratio. The second bracketed term 
represents the difference between measured CSF albumin and expected 
albumin if the blood­brain barrier is intact; 230 is the normal serum/CSF 
albumin ratio. The CSF albumin excess is multiplied by the IgG/albumin 
ratio and the molecular weight ratio of IgG to albumin (0.43) to correct 
for changes in CSF IgG due to increased barrier permeability. The number 
5 converts the result from a concentration to a daily amount, assuming an 
average daily CSF production of 500 mL (i.e., 5 dL). The formula does 
not consider variations in CSF production or Ig consumption. It assumes 
that the IgG/albumin ratio remains constant over various degrees of blood­
brain barrier impairment—a concept that may lead to variable error 
(Lefvert, 1985). The normal reference interval for the synthesis rate is −9.9 
to +3.3 mg/day. Values greater than 8.0 mg/day indicate an increased rate 
(Silverman, 1994).
CSF IgG is normally 3%–5% of total CSF protein, but in multiple 
sclerosis (MS), the concentration approaches that of plasma (15%–18%) 
(Hersey, 1980). The CSF IgG index and the IgG synthesis rate have a 
sensitivity of 90% in patients with definite MS, but the sensitivity is lower 
in patients with possible MS, in whom accuracy is most needed (Marton, 
1986). In addition, the specificity for MS is only moderate because 
increased intrathecal IgG synthesis occurs in many other inflammatory 
neurologic diseases.
The Ig index and synthesis rate calculations may also be applied to 
IgM, IgA, Ig light chains, and specific antibodies to infectious 
microorganisms. For example, increased synthesis of IgM and free κ 
light chains have been suggested as markers for MS (Rudick, 1989; 
Lolli, 1991).
Electrophoretic Techniques. Although the diagnosis of MS is ulti­
mately a clinical one, significant advances have been made in laboratory 
testing for this disorder. CSF total protein is increased in less than 50% 
of patients with MS. Indeed, if the CSF protein exceeds 100 mg/dL, the 
patient probably does not have MS. However, the γ­globulin fraction, as 
determined by CSF electrophoresis, is often increased in MS. Thus, the 
CSF total protein/γ­globulin ratio exceeds 0.12 in about 65% of cases 
(Johnson, 1977). Using electroimmunodiffusion, a CSF IgG/albumin 
ratio greater than 0.25 is present in about 75% of cases (Tourtellotte, 
1971). Furthermore, levels greater than the mean CSF IgG index + 3SD 
are present in 80%–85% of MS cases. However, this upper reference level 
varies significantly between laboratories, and 0.58, 0.66, and 0.77 have 
been reported as cutoff values (Olsson, 1976; Tibbling, 1977; Markowitz, 
1983, respectively). Therefore, laboratories should establish their own 
reference values.
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In children with acute lymphoblastic leukemia, elevated CSF fibronec­
tin levels are associated with a poor prognosis, presumably due to leukemic 
involvement of the CNS (Rautonen, 1989). Significant CSF elevations 
have also been reported in Burkitt’s lymphoma (Rajantie, 1989), some 
metastatic solid tumors, astrocytomas, and bacterial meningitis (Weller, 
1990; Torre, 1991). Decreased levels have been reported in viral meningitis 
and in the acquired immunodeficiency syndrome (AIDS)–dementia 
complex (Torre, 1991, 1993).
β-Amyloid Protein 42 and τ Protein. The diagnosis of Alzheimer’s 
disease (AD) is based on the presence of dementia and a specific clinical 
profile (i.e., from medical history, clinical examination) suggestive of AD, 
together with the exclusion of other causes of dementia. Pathologically, 
the disease is characterized by the presence of neurofibrillary tangles and 
amyloid plaques.
Recent studies indicate that measurement of biochemical markers 
increases diagnosticaccuracy, especially early in the course of the disease, 
when clinical symptoms are mild and vague and overlap with cognitive 
changes that accompany aging and ischemic dementia. Thus, increased 
CSF levels of microtubule­associated τ protein and decreased levels 
of β­amyloid protein ending at amino acid 42 have been shown to 
significantly increase the accuracy of AD diagnosis (Andreasen, 2001; 
Riemenschneider, 2002; Sunderland, 2003). Indeed, the predictive value 
for early AD is greater than 90% (Andreasen, 2001). Others have 
found that the calculated ratio of phosphorylated τ protein to β­amyloid 
peptide is superior to either measure alone (Maddalena, 2003). The 
results were as follows: Distinguishing patients with AD from healthy 
controls—sensitivity 96%, specificity 97%; patients with AD from those 
with non­AD dementia—sensitivity 80%, specificity 73%; and patients 
with AD from those with other neurologic disorders—sensitivity 80%, 
specificity 89%.
Protein 14-3-3. The transmissible spongiform encephalopathies consti­
tute a group of uniformly fatal neurodegenerative diseases. Of these, CJD 
is the major spongiform disease in humans. Two proteins, designated 130 
and 131, have been detected in low concentrations in CSF from CJD 
patients. These proteins have the same amino acid sequence as protein 
14­3­3 (Hsich, 1996). Moreover, in patients with dementia, a positive 
immunoassay for the 14­3­3 protein in CSF strongly supports a diagnosis 
of CJD. In a subsequent study of patients with suspected CJD, the sensitiv­
ity of the 14­3­3 protein determined by immunoassay was 97%, and the 
specificity was 87% (Lemstra, 2000). False­positive results were seen pri­
marily in patients with stroke and meningoencephalitis.
Others, using a modified Western blot technique, reported a 94.7% 
positive predictive value and a 92.4% negative predictive value for CJD 
(Zerr, 1998). False­positive results from a single CSF analysis were seen 
in patients with herpes simplex encephalitis, atypical encephalitis, meta­
static lung cancer, and hypoxic brain damage.
Transferrin and CSF Leakage. Cerebrospinal fluid leakage usually 
presents as otorrhea or rhinorrhea following head trauma, in some cases 
beginning months to years after the injury. Recurrent meningitis is a 
serious complication, making accurate identification of the leaking fluid 
very important. In this regard, protein and glucose measurements are too 
nonspecific to be of value. Transferrin, an iron­binding glycoprotein with 
a molecular mass of about 77 kDa, is synthesized primarily in the liver. 
However, two transferrin isoforms are present in the CSF; the major 
isoform (β1­transferrin) is present in all body fluids. The second isoform 
(β2­transferrin), present only in the central nervous system, is produced in 
the central nervous system by the catalytic conversion of β­1­transferrin 
by neuraminidase. Immunofixation electrophoresis readily identifies both 
isoforms.
Protein electrophoresis with transferrin immunofixation is a noninva­
sive, rapid, and inexpensive test of high sensitivity and specificity that 
requires as little as 0.1 mL of fluid (Ryall, 1992; Normansell, 1994). Several 
reports have demonstrated the value of this technique in the diagnosis 
of CSF otorrhea and rhinorrhea—conditions in which both isoforms 
are readily identified (Irjala, 1979; Rouah, 1987; Zaret, 1992). Others 
have stressed the importance of β2­transferrin identification in both CSF 
and inner ear perilymphatic leakage, as well as possible sources of error 
due to the presence of a transferrin allelic variant (Skedros, 1993a,b; 
Sloman, 1993).
Methemoglobin and Bilirubin. Although most cases of subarachnoid 
and intracerebral hemorrhage are readily identified by computed 
Myelin Basic Protein. Myelin basic protein (MBP), a component of the 
myelin nerve sheath, is released during demyelination as a result of various 
neurologic disorders, especially MS. Thus, MBP has been shown to posi­
tively correlate with CSF leukocyte count, intrathecal IgG synthesis, and 
the CSF/serum albumin concentration quotient (Sellebjerg, 1998). These 
results support the use of MBP in CSF as a surrogate disease marker during 
acute MS exacerbations. Others have found that analysis of antibody 
against MBP in patients with a clinically isolated syndrome is a rapid and 
precise method for predicting early conversion to clinically definite MS 
(Berger, 2003). However, increased CSF levels have also been reported 
in Guillain­Barré syndrome, lupus erythematosus, subacute sclerosing 
panencephalitis, and various brain tumors, and following CNS irradiation 
and chemotherapy (Brooks, 1989; Mahoney, 1984). Measurement of CSF 
levels has also been proposed as a prognostic marker in patients with 
serious head injury (Noseworthy, 1985).
α2-Macroglobulin. Except for a small amount transported across the 
BBB in pinocytic vesicles, α2­macroglobulin (A2M) is normally excluded 
from the CSF because of its large size. The number of these vesicles is 
increased in certain polyneuropathies, resulting in an increased CSF A2M 
level. Significant elevation reflects subdural hemorrhage or breakdown of 
the BBB, as occurs in bacterial meningitis. A2M measurement alone, or in 
relationship to albumin and IgG, may assist in the evaluation of neurologic 
disorders and increased CSF protein, and in the rapid differentiation 
between bacterial and aseptic meningitis (Meucci, 1993; Kanoh, 1997).
β2-Microglobulin. This protein is part of the human leukocyte antigen 
class I molecule on the surfaces of all nucleated cells. CSF levels above 
1.8 mg/L are associated with leptomeningeal leukemia and lymphoma 
but are not highly specific (Weller, 1992), in that they have a maximal 
positive predictive value of 78% in cases with a positive cytology (Jeffrey, 
1990). β2­microglobulin (B2M) was also recently shown to be a marker for 
neuro­Behçet’s syndrome (Kawai, 2000). Moreover, viral infections, 
including human immunodeficiency virus (HIV)­1, other inflammatory 
conditions, and various malignancies have also been associated with ele­
vated levels. However, the measurement of B2M remains primarily 
investigational.
C-Reactive Protein. Early studies indicated that CSF C­reactive protein 
(CRP) is useful in differentiating viral (aseptic) meningitis from bacterial 
meningitis (Corral, 1981; Abramson, 1985; Stearman, 1994). Others have 
reported that CSF CRP is a more useful screening test for viral versus 
bacterial meningitis, especially in children (Sormunen, 1999). A meta­
analysis of CRP studies since 1980 suggested that a normal CSF or serum 
CRP has a high probability of ruling out bacterial meningitis (i.e., negative 
predictive value about 97%) (Gerdes, 1998). Moreover, a recent study 
found not only that CSF CRP levels were increased in bacterial meningitis, 
but that these levels were significantly higher in patients with gram­
negative bacterial meningitis than in those with gram­positive bacterial 
meningitis (Rajs, 2002).
Fibronectin. This large glycoprotein (molecular mass about 420 kDa) is 
normally present in essentially all tissues and body fluids. Its primary func­
tion is its role in cell adhesion and phagocytosis (Ruoslahti, 1981). Thus, 
cell adhesion allows leukocytes to adhere to and pass through the vascular 
endothelia and migrate to the inflammatory site.
TABLE 29-12 
CSF Proteins and Central Nervous System Diseases
Protein Major diseases/disorders
α2-Macroglobulin Subdural hemorrhage, bacterial meningitis
β-Amyloid and τ proteins Alzheimer’s disease
β2-Microglobulin Leukemia/lymphoma, Behçet’s syndrome
C-reactive protein Bacterial and viral meningitis
Fibronectin Lymphoblastic leukemia, AIDS, meningitis
Methemoglobin Mild subarachnoid/subdural hemorrhage
Myelin basic protein Multiple sclerosis, tumors, others
Protein 14-3-3Creutzfeldt-Jakob disease
Transferrin CSF leakage (otorrhea, rhinorrhea)
AIDS, Acquired immunodeficiency syndrome; CSF, cerebrospinal fluid.
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Adenosine Deaminase
Adenosine deaminase (ADA) catalyzes the irreversible hydrolytic deamina­
tion of adenosine to produce inosine. Because ADA is particularly abun­
dant in T lymphocytes, which are increased in tuberculosis, its measurement 
has been recommended in the diagnosis of pleural, peritoneal, and men­
ingeal tuberculosis. Higher ADA levels are present in tuberculous infec­
tions than in viral, bacterial, and malignant diseases (Blake, 1982; Mann, 
1982, Choi, 2002), although the degree of increase indicative of tubercu­
lous infection varies depending on the specific assay used. ADA appears to 
have limited utility in HIV­associated neurologic disorders (Corral, 2004).
Creatine Kinase
Brain tissue is rich in creatine kinase (CK) because it participates in main­
taining an adequate supply of adenosine triphosphate. Increased CSF CK 
activity has been reported in numerous CNS disorders, including hydro­
cephalus, cerebral infarction, various primary brain tumors, and subarach­
noid hemorrhage, among others (Savory, 1979). In patients with head 
trauma, CSF CK levels correlate directly with the severity of the concus­
sion (Florez, 1976).
CSF CK­MM and CK­MB are not normally present; when identified, 
they are due to blood contamination (CK­MM) and an equilibrium 
between CK­BB and CK­MM to produce CK­MB. Because the CK­BB 
isoenzyme accounts for about 90% of brain CK activity and mitochondrial 
CK (CKmt) the other 10%, CK isoenzyme measurements are more spe­
cific than total CK for CNS disorders (Chandler, 1984).
CSF CK­BB is increased about 6 hours following an ischemic or 
anoxic insult. Global brain ischemia following respiratory or cardiac arrest 
results in diffuse cerebral injury with peak CK­BB levels in about 48 hours 
(Chandler, 1986). Here, CSF CK­BB activity less than 5 U/L (upper 
normal level) indicates minimal neurologic damage; 5–20 U/L indicates 
mild to moderate CNS injury; and levels between 21 and 50 U/L are 
commonly correlated with death. Death occurs in essentially all patients 
with levels above 50 U/L.
Increased CSF CK­BB levels are also associated with the outcome fol­
lowing a subarachnoid hemorrhage (Coplin, 1999). Here, a CK­BB level 
greater than 40 U/L increased the chance of an unfavorable early or late 
outcome to 100%. The death rate was 13% when the CSF CK­BB level 
was less than 40 U/L.
Lactate Dehydrogenase
Lactate dehydrogenase (LD) activity is high in brain tissue, with a pre­
dominance of the electrophoretically fast­moving isoenzyme fractions LD1 
and LD2. Total LD activity of 40 U/L is a reasonable upper limit of normal 
for adults and 70 U/L for neonates (Donald, 1986; Engelke, 1986). LD is 
useful in differentiating a traumatic tap from intracranial hemorrhage 
because a current traumatic tap with intact RBCs does not significantly 
elevate the LD level (Engelke, 1986). Sensitivity and specificity are about 
70%–85% depending on the cutoff value. As with lactate, LD activity is 
significantly higher in bacterial meningitis than in aseptic meningitis 
(Donald, 1986; Engelke, 1986). Using a cutoff of 40 U/L, the sensitivity 
is about 86% and the specificity about 93%.
Total CSF LD levels are also increased in patients with CNS leukemia, 
lymphoma, metastatic carcinoma, bacterial meningitis, and subarachnoid 
hemorrhage (Kjeldsberg, 1993). CSF LD isoenzymes have been shown to 
add considerable specificity in the evaluation of various metastatic brain 
tumors (Fleisher, 1981). Thus, the LD5/total LD ratio is increased (i.e., 
above 10%–15%) in patients with leptomeningeal metastases from carci­
noma of the breast and lung and malignant melanoma. Isoenzyme analysis 
also shows a distinct pattern in young children with infantile spasms 
(Nussinovitch, 2003a) and febrile convulsions (Nussinovitch, 2003b). 
Compared with controls, both disorders are characterized by decreased 
LD1, increased LD2 and LD3, and no changes in LD4 and LD5.
CT is of limited value in estimating recovery potential and neurologic 
outcome during the early stages of ischemic brain injury. However, com­
pared with controls (mean LD, 11.2 U/L), patients with an early stroke 
had a mean level of 40.9 U/L, and those with a transient ischemic attack 
(TIA) had a mean value of 11.8 U/L (Lampl, 1990). Moreover, in patients 
with hypoxic brain injury, an increased LD level 72 hours following resus­
citation indicates a poor prognosis (Karkela, 1992).
Lysozyme
Lysozyme (muramidase) catalyzes the depolymerization of mucopolysac­
charides. Because the enzyme is particularly rich in neutrophil and mac­
rophage lysosomes, its activity is very low in normal CSF. However, CSF 
lysozyme activity is significantly increased in patients with both bacterial 
tomography (CT), patients with mild subarachnoid hemorrhage, small 
subdural or cerebral hematomas, and blood seepage from an aneurysm or 
neoplasm and from small cerebral infarcts often are not identified by this 
technique. In these cases, CSF spectrophotometric analysis has been 
shown to detect methemoglobin in colorless CSF (<0.3 µmol/L) 
(Trbojevic­Cepe, 1992). However, an increase in CSF bilirubin is now 
recognized as the key finding supporting the diagnosis of subarachnoid 
hemorrhage (UK National External Quality Assessment Scheme for 
Immunochemistry Working Group, 2003). Thus, a single net bilirubin 
absorbance cutoff point of >0.007 absorbance units is recommended in the 
decision tree for interpretation and reporting of results.
Glucose
Derived from blood glucose, fasting CSF glucose levels are normally 
50–80 mg/dL (2.8–4.4 mmol/L)—about 60% of plasma values. Results 
should be compared with plasma levels, ideally following a 4­hour fast, for 
adequate clinical interpretation. The normal CSF/plasma glucose ratio 
varies from 0.3–0.9, with fluctuations in blood levels caused by the lag in 
CSF glucose equilibration time.
CSF values below 40 mg/dL (2.2 mmol/L) or ratios below 0.3 are 
considered to be abnormal. Hypoglycorrhachia is a characteristic finding 
of bacterial, tuberculous, and fungal meningitis. However, sensitivity can 
be as low as 55% for bacterial meningitis (Hayward, 1987), so a normal 
level does not exclude these conditions. Some cases of viral meningoen­
cephalitis also have low glucose levels, but generally not to the degree seen 
in bacterial meningitis. Meningeal involvement by a malignant tumor, 
sarcoidosis, cysticercosis, trichinosis, ameba (Naegleria), acute syphilitic 
meningitis, intrathecal administration of radioiodinated serum albumin, 
subarachnoid hemorrhage, symptomatic hypoglycemia, and rheumatoid 
meningitis may also produce low CSF glucose levels (Fishman, 1992).
Decreased CSF glucose results from increased anaerobic glycolysis in 
brain tissue and leukocytes and from impaired transport into the CSF. 
Bacteria are usually present in insufficient quantities to be a major con­
tributor. CSF glucose levels normalize before protein levels and cell counts 
during recovery from meningitis, making it a useful parameter in assessing 
response to treatment.
Increased CSF glucose is of no clinical significance, reflecting 
increased blood glucose levels within 2 hours of lumbar puncture. A trau­
matic tap may also cause a spurious increase in CSF glucose.
Lactate
CSF and blood lactate levels are largely independent of each other. 
The reference interval for older children and adults is 9.0–26 mg/dL 
(1.0–2.9 mmol/L) (Knight, 1981). Newborns have higher levels, ranging 
from about 10–60 mg/dL (1.1–6.7 mmol/L) for the first 2 days, and from 
10–40 mg/dL (1.1–4.4 mmol/L) for days 3 to 10 (McGuinness, 1983). 
Elevated CSF lactate levels reflect CNS anaerobic metabolism due to 
tissue hypoxia.Lactate measurement has been used as an adjunctive test in differentiat­
ing viral meningitis from bacterial, mycoplasma, fungal, and tuberculous 
meningitis, in which routine parameters yield equivocal results. In patients 
with viral meningitis, lactate levels are usually below 25 mg/dL (2.8 mmol/L) 
and are almost always less than 35 mg/dL (3.9 mmol/L), whereas bacterial 
meningitis typically has levels above 35 mg/dL (Bailey, 1990; Cameron, 
1993). Using 30–36 mg/dL as the cutoff value for bacterial meningitis, the 
sensitivity and specificity are about 80% and 90%, respectively. Viral men­
ingitis, partially treated bacterial meningitis, and tuberculous meningitis 
often have intermediate lactate levels that overlap each other, limiting the 
use of lactate measurements in this differential diagnosis.
Persistently elevated ventricular CSF lactate levels are associated with 
a poor prognosis in patients with severe head injury (DeSalles, 1986).
F2-Isoprostanes
F2­isoprostanes are increased in diseased regions of the brain in patients 
with AD (Pratico, 1998). Compared with age­matched controls, CSF 
F2­isoprostanes are also elevated in patients with probable AD (Montine, 
1999). Therefore, in conjunction with CSF τ and β­amyloid protein, the 
measurement of CSF F2­isoprostanes appears to enhance the accuracy of 
the laboratory diagnosis of AD (Montine, 2001).
Enzymes
A wide variety of enzymes derived from brain tissue, blood, or cellular 
elements have been described in the CSF. Although CSF enzyme assays 
are not commonly used in the diagnosis of CNS diseases, there are 
diseases/disorders in which they may prove useful.
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the value of most of these tests in routine clinical practice has not been 
established.
Carcinoembryonic Antigen
Carcinoembryonic antigen (CEA) is an oncofetal protein produced by 
a variety of carcinomas. An early study found increased CEA levels in 
44% of patients with metastatic brain tumors (Suzuki, 1980). Others 
reported that CSF levels of CEA have a sensitivity of only about 31%, 
although the specificity is about 90% for detecting metastatic carcinoma 
of the leptomeninges (Klee, 1986; Twijnstra, 1986). Recently, CSF levels 
of CEA in patients with benign, primary malignant, and metastatic brain 
tumors were 0.31 ng/mL, 0.92 ng/mL, and 6.3 ng/mL, respectively 
(Batabyal, 2003).
Other oncofetal proteins include human chorionic gonadotropin 
(hCG), produced by choriocarcinoma and malignant germ cell tumors 
with a trophoblastic component, and α-fetoprotein, a glycoprotein pro­
duced by yolk sac elements of germ cell tumors. Results of a recent study 
revealed that both β­hCG and α­fetoprotein may be useful in the diagnosis 
and monitoring of the response to therapy in patients with CNS germ cell 
tumors (Seregni, 2002).
Elevation of CSF ferritin is a sensitive indicator of CNS malignancy 
but has very low specificity because it is also increased in patients with 
inflammatory neurologic diseases (Zandman­Goddard, 1986).
MICROBIOLOGICAL EXAMINATION
A thorough and prompt examination of cerebrospinal fluid is essential for 
the diagnosis of CNS infection because an inaccurate or delayed report 
may result in significant mortality or morbidity. Although changes in 
opening pressure, total cell and differential counts, total protein, and 
glucose suggest an infectious origin (Table 29­13), Gram stain and culture 
are critical for a definitive diagnosis.
Bacterial Meningitis
The most common agents of bacterial meningitis are group B streptococ­
cus (neonates), Neisseria meningitidis (3 months and older) (Fig. 29­9), 
Streptococcus pneumoniae (3 months and older), Escherichia coli and other 
gram­negative bacilli (newborn–1 month), Haemophilus influenzae (3 
months–18 years), and Listeria monocytogenes (neonates, elderly, alcoholics, 
and immunosuppressed) (Graves, 1989; Wenger, 1990). H. influenzae, once 
and tuberculous meningitis. Thus, discriminant analysis demonstrated that 
97% of patients with bacterial meningitis had increased lysozyme levels 
(Ribeiro, 1992). Others found that patients with tuberculous meningitis 
had significantly higher CSF lysozyme levels than those with bacterial 
meningitis, partially treated bacterial meningitis, and controls (Mishra, 
2003). The diagnostic sensitivity and specificity for tuberculous meningitis 
were 93.7% and 84.1%, respectively. Increased levels are also present in 
cerebral atrophy, various CNS tumors, multiple sclerosis, intracranial 
hemorrhage, and epilepsy (Kjeldsberg, 1993).
Ammonia, Amines, and Amino Acids
CSF ammonia levels vary from 30%–50% of blood values. Elevated levels 
are generally proportional to the degree of existing hepatic encephalopathy 
but are difficult to quantify. Moreover, because hepatic encephalopathy 
generally correlates with blood ammonia levels, the measurement of CSF 
ammonia has little, if any, clinical value. However, cerebral glutamine, 
synthesized from ammonia and glutamic acid, serves as the means for CNS 
ammonia removal. Thus, CSF glutamine levels reflect the concentration 
of brain ammonia. Glutamine reference intervals are method dependent; 
the upper reference level is about 20 mg/dL. Values over 35 mg/dL are 
usually associated with hepatic encephalopathy (Fishman, 1992). Elevated 
CSF glutamine levels have also been reported in patients with encepha­
lopathy secondary to hypercapnia and sepsis (Mizock, 1989).
A major etiologic theory of schizophrenia involves dopamine. The 
cornerstone for this theory is the fact that neuroleptic drugs that block 
dopamine receptors are effective in the treatment of this disorder. Thus, 
it has been reported that CSF levels of homovanillic acid (HVA), a metabo­
lite of the biogenic amines, are related to the severity of schizophrenic 
psychosis (Maas, 1997). However, HVA concentration varied as a function 
of psychosis rather than being related to the diagnosis of schizophrenia 
per se. Others reported decreased CSF levels of 5­hydroxyindoleacetic 
acid, a metabolite of serotonin, in schizophrenic patients with suicidal 
behavior (Cooper, 1992). This report adds support for a possible relation­
ship between suicide and CNS serotonin metabolism.
Although free CSF amino acids are relatively high in infants younger 
than 30 days of age, their concentration is further increased in those with 
febrile convulsions and bacterial meningitis. γ­Aminobutyric acid (GABA), 
a major inhibitory brain transmitter, is significantly decreased in basal 
ganglia neurons, and is very low or undetectable in the CSF of patients 
with Alzheimer’s disease and Huntington’s disease (Achar, 1976; Dubowitz, 
1992). In addition, CSF GABA was detected in all patients with migraine 
attacks, but not in those with tension headaches or in the control group 
without headaches (Welch, 1975). Conversely, infants with startle disease, 
a rare inherited autosomal dominant disorder characterized by seizures or 
the so­called stiff baby syndrome, have significantly decreased CSF 
GABA levels (Dubowitz, 1992; Berthier, 1994).
Electrolytes and Acid-Base Balance
There are no clinically useful indications for the measurement of CSF 
sodium, potassium, chloride, calcium, or magnesium. Measurements of 
CSF pH, partial pressure of carbon dioxide (pCO2), and bicarbonate are 
also not practical for patient care (Fishman, 1992).
Tumor Markers
Numerous studies have shown that various tumor markers are increased 
in the CSF of patients with both primary and metastatic tumors. However, 
TABLE 29-13 
Typical Lumbar CSF Findings in Meningitis
Test Bacterial Viral Fungal Tuberculous
Opening pressure Elevated Usually normal Variable Variable