SEPTEMBER 15, 2003 / VOLUME 68, NUMBER 6 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1103
pressure, and cautioned not to hyperventilate,
because hyperventilating will lower the open-
Normal opening pressure ranges from 10 to
100 mm H
0 in young children, 60 to 200 mm
0 after eight years of age, and up to 250 mm
0 in obese patients.
sion is defined as an opening pressure of less
than 60 mm H
0. This finding is rare except in
patients with a history of trauma causing a
CSF leak, or whenever the patient has had a
previous lumbar puncture.
Opening pressures above 250 mm H
diagnostic of intracranial hypertension. Ele-
vated intracranial pressure is present in many
pathologic states, including meningitis,
intracranial hemorrhage, and tumors. Idio-
pathic intracranial hypertension is a condition
most commonly seen in obese women during
their childbearing years. When an elevated
opening pressure is discovered, CSF should be
removed slowly and the pressure monitored
during the procedure. No additional CSF
should be removed once the pressure reaches
50 percent of the opening pressure.
rimary care physicians frequently
perform lumbar puncture, be-
cause cerebrospinal fluid (CSF) is
an invaluable diagnostic window
to the central nervous system
(CNS). Commonly performed tests on CSF
include protein and glucose levels, cell counts
and differential, microscopic examination,
and culture. Additional tests such as opening
pressure, supernatant color, latex agglutina-
tion, and polymerase chain reaction also may
be performed. Knowing which tests to order
and how to interpret them allows physicians
to use CSF as a key diagnostic tool in a vari-
ety of diseases.
To measure CSF opening pressure, the
patient must be in the lateral decubitus posi-
tion with the legs and neck in a neutral posi-
tion. The meniscus will fluctuate between 2
and 5 mm with the patient’s pulse and
between 4 and 10 mm with respirations.
patient should be advised not to strain,
because straining can increase the opening
Lumbar puncture is frequently performed in primary care. Properly interpreted tests can
make cerebrospinal fluid (CSF) a key tool in the diagnosis of a variety of diseases. Proper eval-
uation of CSF depends on knowing which tests to order, normal ranges for the patient’s age,
and the test’s limitations. Protein level, opening pressure, and CSF-to-serum glucose ratio
vary with age. Xanthochromia is most often caused by the presence of blood, but several
other conditions should be considered. The presence of blood can be a reliable predictor of
subarachnoid hemorrhage but takes several hours to develop. The three-tube method, com-
monly used to rule out a central nervous system hemorrhage after a “traumatic tap,” is not
completely reliable. Red blood cells in CSF caused by a traumatic tap or a subarachnoid hem-
orrhage artificially increase the white blood cell count and protein level, thereby confound-
ing the diagnosis. Diagnostic uncertainty can be decreased by using accepted corrective for-
mulas. White blood cell differential may be misleading early in the course of meningitis,
because more than 10 percent of cases with bacterial infection will have an initial lympho-
cytic predominance and viral meningitis may initially be dominated by neutrophils. Culture is
the gold standard for determining the causative organism in meningitis. However, poly-
merase chain reaction is much faster and more sensitive in some circumstances. Latex agglu-
tination, with high sensitivity but low specificity, may have a role in managing partially
treated meningitis. To prove herpetic, cryptococcal, or tubercular infection, special staining
techniques or collection methods may be required. (Am Fam Physician 2003;68:1103-8. Copy-
right© 2003 American Academy of Family Physicians.)
Cerebrospinal Fluid Analysis
DEAN A. SEEHUSEN, M.D., MARK M. REEVES, M.D., and DEMITRI A. FOMIN, M.D.
Tr ipler Army Medical Center, Honolulu, Hawaii
See page 1039 for
definitions of strength-
Normal CSF is crystal clear. However, as few
as 200 white blood cells (WBCs) per mm
400 red blood cells (RBCs) per mm
CSF to appear turbid. Xanthochromia is a yel-
low, orange, or pink discoloration of the CSF,
most often caused by the lysis of RBCs result-
ing in hemoglobin breakdown to oxyhemo-
globin, methemoglobin, and bilirubin. Discol-
oration begins after RBCs have been in spinal
fluid for about two hours, and remains for two
to four weeks.
Xanthochromia is present in
more than 90 percent of patients within
12 hours of subarachnoid hemorrhage onset
and in patients with serum bilirubin levels
between 10 to 15 mg per dL (171 to 256.5
µmol per L). CSF protein levels of at least 150
mg per dL (1.5 g per L)—as seen in many
infectious and inflammatory conditions, or as
a result of a traumatic tap that contains more
than 100,000 RBCs per mm
—also will result
Newborn CSF is often
xanthochromic because of the frequent eleva-
tion of bilirubin and protein levels in this age
group. Table 1 lists CSF colors associated with
Normal CSF may contain up to 5 WBCs per
in adults and 20 WBCs per mm
Eighty-seven percent of patients with
bacterial meningitis will have a WBC count
higher than 1,000 per mm,
while 99 percent
will have more than 100 per mm
than 100 WBCs per mm
is more common in
patients with viral meningitis.
Elevated WBC counts also may occur after a
in intracerebral hemorrhage, with
malignancy, and in a variety of inflammatory
conditions. Tab l e 2 lists common CSF findings
in various types of meningitis.
Peripheral blood in the CSF after a “trau-
matic tap” will result in an artificial increase
in WBCs by one WBC for every 500 to
1,000 RBCs in the CSF. This correction factor
is accurate as long as the peripheral WBC
count is not extremely high or low.
A traumatic tap occurs in approximately
20 percent of lumbar punctures. Common
practice is to measure cell counts in three
consecutive tubes of CSF. If the number of
RBCs is relatively constant, then it is assumed
that the blood is caused by an intracranial
1104 AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 68, NUMBER 6 / SEPTEMBER 15, 2003
Cerebrospinal Fluid Supernatant Colors
and Associated Conditions or Causes
Color of CSF
supernatant Conditions or causes
Yellow Blood breakdown products
CSF protein ≥150 mg per dL
(1.5 g per L)
>100,000 red blood cells per mm
Orange Blood breakdown products
High carotenoid ingestion
Pink Blood breakdown products
Brown Meningeal melanomatosis
CSF = cerebrospinal fluid.
Information from references 2, 4, and 5.
DEAN A. SEEHUSEN, M.D., is a faculty development fellow in the Department of Fam-
ily Practice at Madigan Army Medical Center, Tacoma, Wash. He formerly was a staff
physician in the Department of Family Practice and Emergency Medical Services at
Tripler Army Medical Center, Honolulu. He earned his medical degree from the Uni-
versity of Iowa College of Medicine, Iowa City, and completed a residency in family
practice at Tripler Army Medical Center.
MARK M. REEVES, M.D., is director of the family practice residency program at Tripler
Army Medical Center. He earned his medical degree from the Uniformed Services Uni-
versity of the Health Sciences, Bethesda, Md., and completed a residency in family
practice at Dwight D. Eisenhower Army Medical Center, Augusta, Ga.
DEMITRI A. FOMIN, M.D., is a staff neurologist in the Department of Medicine, neu-
rology service, at Tripler Army Medical Center. He earned his medical degree from the
Uniformed Services University of the Health Sciences and completed a residency in
neurology at Walter Reed Army Medical Center, Washington, D.C.
Address correspondence to Dean A. Seehusen, M.D., 5803 152nd Ave. Ct. E, Sumner,
WA 98390 (e-mail: email@example.com). Reprints are not available from the authors.
Xanthochromia is present in more than 90 percent of
patients within 12 hours of subarachnoid hemorrhage onset.
hemorrhage. A falling count is attributed to a
traumatic tap. The three-tube method, how-
ever, is not always reliable.
Xanthochromia is a more reliable predictor
of hemorrhage. If a traumatic tap occurs
within 12 hours of a suspected subarachnoid
hemorrhage, it is reasonable to repeat the
lumbar puncture one interspace up to try and
obtain clear CSF.
The WBC count seen in normal adult CSF is
comprised of approximately 70 percent lym-
phocytes and 30 percent monocytes. Occa-
sionally, a solitary eosinophil or polymor-
phonucleocyte (PMN) will be seen in normal
Several PMNs in a neonatal patient’s CSF
is not unusual.
The majority of patients with Guillain-
Barré syndrome will have 10 or fewer mono-
cytes per mm
and a minority of patients will
have 11 to 50 monocytes per mm
50 monocytes per mm
are seen in about
25 percent of patients with multiple sclerosis.
The cell differential alone cannot differentiate
between bacterial and nonbacterial meningi-
tis. Lymphocytosis is seen in viral, fungal, and
tuberculous infections of the CNS, although a
predominance of PMNs may be present in the
early stages of these infections. CSF in bacter-
ial meningitis is typically dominated by the
presence of PMNs. However, more than
10 percent of bacterial meningitis cases will
show a lymphocytic predominance, especially
early in the clinical course and when there are
fewer than 1,000 WBCs per mm
Eosinophilic meningitis is defined as more
than 10 eosinophils per mm
or a total CSF
cell count made up of more than 10 percent
eosinophils. Parasitic infection should be sus-
pected in this situation. Other possible causes
may include viral, fungal, or rickettsial menin-
gitis; having ventriculoperitoneal shunts with
or without coexisting infection; malignancy;
and adverse drug reactions.
Gram stain is positive in 60 to 80 percent of
untreated cases of bacterial meningitis and in
40 to 60 percent of partially treated cases. The
sensitivity according to the causative organism
ranges from 90 percent in pneumococcal or
SEPTEMBER 15, 2003 / VOLUME 68, NUMBER 6 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1105
Typical Cerebrospinal Fluid Findings in Various Types of Meningitis
Test Bacterial Viral Fungal Tubercular
Opening pressure Elevated Usually normal Variable Variable
White blood cell count ≥1,000 per mm
<100 per mm
Cell differential Predominance of Predominance of Predominance Predominance
PMNs* lymphocytes† of lymphocytes of lymphocytes
Protein Mild to marked Normal to elevated Elevated Elevated
CSF-to-serum glucose Normal to marked Usually normal Low Low
CSF = cerebrospinal fluid; PMNs = polymorphonucleocytes.
*—Lymphocytosis present 10 percent of the time.
†—PMNs may predominate early in the course.
Information from references 2, 10, 17, and 20.
staphylococcal meningitis to less than 50 per-
cent in Listeria meningitis. Hyphae can occa-
sionally be seen in Candida or other fungal
Several factors influence the sensitivity of
Gram stain. Laboratory techniques used to
concentrate and stain CSF can greatly influ-
ence reliability. Cytocentrifugation increases
the ability to detect bacteria.
bers of colony-forming units (CFU) per mm
of CSF increase the likelihood of a positive
result. Staining will be positive in 25 percent of
cases if fewer than 1,000 CFU per mm
present, and in 75 percent of cases if more
than 100,000 CFU per mm
Lastly, the experience of laboratory personnel
is very important. Up to 10 percent of initial
Gram stains are misread.
Acid-fast staining should be done if tuber-
culosis is clinically suspected. Only 37 per-
cent of initial smears will be positive for acid-
fast bacilli. This result can be increased to
87 percent if four smears are done.
tivity also can be increased by examining the
Other stains should be performed if indi-
cated by the situation. Cryptococcus may be
identified up to 50 percent of the time on an
India ink preparation. A tap-water control
should always be done to ensure that the India
ink is not contaminated.
Toxoplasmosis can be diagnosed with
Wright or Giemsa stain. A simple wet prepa-
ration of CSF under a cover slip can yield pos-
itive results in a variety of protozoan and
CSF protein concentration is one of the
most sensitive indicators of pathology within
the CNS. Newborn patients have up to 150 mg
per dL (1.5 g per L) of protein.
range of 18 to 58 mg per dL (0.18 to 0.58 g per
L) is reached between six and 12 months of
The physician should know what the
normal reference range is for his or her labo-
ratory,because the measurement is somewhat
Elevated CSF protein is seen in infections,
intracranial hemorrhages, multiple sclerosis,
Guillain Barré syndrome, malignancies, some
endocrine abnormalities, certain medication
use, and a variety of inflammatory conditions
(Table 3).Protein concentration is falsely ele-
vated by the presence of RBCs in a traumatic
tap situation. This can be corrected by sub-
tracting 1 mg per dL (0.01 g per L) of protein
for every 1,000 RBCs per mm
level B: observational study] This correction is
only accurate if the same tube is used for the
protein and cell counts.
Low CSF protein levels can occur in condi-
tions such as repeated lumbar puncture or a
chronic leak, in which CSF is lost at a higher
than normal rate.
Low CSF protein levels also
are seen in some children between the ages of
six months and two years, in acute water intox-
ication, and in a minority of patients with idio-
pathic intracranial hypertension. CSF protein
levels do not fall in hypoproteinemia.
A true normal range cannot be given for
CSF glucose. As a general rule, CSF glucose is
AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 68, NUMBER 6 / SEPTEMBER 15, 2003
Average and Range of Cerebrospinal Fluid Protein
Condition per dL (g per L) Range: mg per dL (g per L)
Bacterial meningitis 418 (4.18) 21 to 2220 (0.21 to 22.2)
Brain tumor 115 (1.15) 15 to 1920 (0.15 to 19.2)
Brain abscess 69 (0.69) 16 to 288 (0.16 to 2.88)
Aseptic meningitis 77 (0.77) 11 to 400 (0.11 to 4.0)
Multiple sclerosis 43 (0.43) 13 to 133 (0.13 to 1.33)
Cerebral hemorrhage 270 (2.7) 19 to 2110 (0.19 to 21.1)
Epilepsy 31 (0.31) 7 to 200 (0.07 to 2.0)
Acute alcoholism 32 (0.32) 13 to 88 (0.13 to 0.88)
Neurosyphilis 68 (0.68) 15 to 4200 (0.15 to 42.0)
Adapted with permission from Fishman RA. Cerebrospinal fluid in diseases of the
nervous system. 2d ed. Philadelphia: Saunders, 1992.
about two thirds of the serum glucose mea-
sured during the preceding two to four hours
in a normal adult. This ratio decreases with
increasing serum glucose levels. CSF glucose
levels generally do not go above 300 mg per dL
(16.7 mmol per L) regardless of serum levels.
Glucose in the CSF of neonates varies much
more than in adults, and the CSF-to-serum
ratio is generally higher than in adults.
CNS infections can cause lowered CSF glu-
cose levels, although glucose levels are usually
normal in viral infections (Table 2).
glucose levels do not rule out infection,
because up to 50 percent of patients who have
bacterial meningitis will have normal CSF
Chemical meningitis, inflammatory condi-
tions, subarachnoid hemorrhage, and hypo-
glycemia also cause hypoglycorrhachia (low
glucose level in CSF). Elevated levels of glu-
cose in the blood is the only cause of having an
elevated CSF glucose level. There is no patho-
logic process that causes CSF glucose levels to
Cultures done on 5 percent sheep blood
agar and enriched chocolate agar remain the
gold standards for diagnosing bacterial
Antibiotic treatment prior to
lumbar puncture can decrease the sensitivity
of culture, especially when given intra-
venously or intramuscularly.
Enterovirus, the leading cause of viral
meningitis, can be recovered in 40 to 80 per-
cent of cases. Culture for herpes simplex virus
is 80 to 90 percent sensitive but can take five to
seven days to become positive.
viral cultures rarely change the initial manage-
ment of meningitis.
Mycobacterium tuberculosis is best grown
using multiple large volume samples of CSF.
At least 15 mL and preferably 40 to 50 mL of
CSF are recommended. Culture is positive
56 percent of the time on the first sample,
and improved to 83 percent of the time if
four separate samples are cultured. These
cultures often take up to six weeks for posi-
Fungal cultures are positive in more than
95 percent of Cryptococcus neoformans cases
and in 66 percent of candidal meningitis
cases. Other fungi are less likely to be culture
Similar to tuberculous meningitis,
culture yield in fungal meningitis can be
increased by obtaining large volumes of CSF
via repeated lumbar punctures.
Latex agglutination (LA) allows rapid de-
tection of bacterial antigens in CSF. Sensitivity
varies greatly between bacteria. LA for
Haemophilus influenzae has a sensitivity of 60
to 100 percent, but is much lower for other
bacteria. The specificity for LA is very low.
However, LA can be useful in partially treated
meningitis cases where cultures may not yield
Because false positives lead to
unnecessary treatment, LA is not routinely
used today. Some experts suggest using LA in
cases of suspected bacterial meningitis if the
initial Gram stain and bacterial culture are
negative after 48 hours.
Polymerase Chain Reaction
Polymerase chain reaction (PCR) has been
a great advance in the diagnosis of meningitis.
PCR has high sensitivity and specificity for
many infections of the CNS, is fast, and can be
done with small volumes of CSF. Although
testing is expensive, there is a potential for cost
savings by decreasing overall diagnostic test-
ing and intervention.
PCR has been especially useful in the diag-
nosis of viral meningitis. PCR of the CSF has
a sensitivity of 95 to 100 percent, and a sensi-
tivity of 100 percent for herpes simplex virus
type 1, Epstein-Barr virus, and enterovirus.
SEPTEMBER 15, 2003 / VOLUME 68, NUMBER 6 www.aafp.org/afp AMERICAN FAMILY PHYSICIAN 1107
Cultures of cerebrospinal fluid are still the gold standard for
confirming the diagnosis of bacterial meningitis.
PCR is faster and more sensitive than culture
for enterovirus meningitis.
When PCR is
positive for enterovirus, it allows earlier hospi-
tal discharge and less intervention.
dence level B: retrospective chart review]
PCR is the most sensitive means of diag-
nosing CMV infections of the CNS,
has been suggested that PCR should replace
brain biopsy as the gold standard for herpes
PCR has a sensitivity of 54 to 100 percent
and a specificity of 94 to 100 percent for
tuberculous meningitis, and could replace
acid-fast bacillus smear and culture as the test
PCR is sensitive for acute neu-
rosyphilis but not for more chronic forms.
PCR also is being studied as a diagnostic tool
for bacterial meningitis and other infections
of the CNS.
The opinions and assertions contained herein are
the private views of the authors and are not to be
construed as official or as reflecting the views of the
U.S. Army Medical Corps or the U.S. Army at large.
The authors indicate that they do not have any con-
flicts of interest. Sources of funding: none reported.
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1108 AMERICAN FAMILY PHYSICIAN www.aafp.org/afp VOLUME 68, NUMBER 6 / SEPTEMBER 15, 2003
Polymerase chain reaction testing has proved to be especially
useful in the diagnosis of viral meningitis.