Merck Manual

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CSF Findings in Meningitis

CSF Findings in Meningitis


Predominant Cell Type*



Specific Tests

Normal CSF

All lymphocytes† (0–5 cells/mcL)

< 40 mg/dL

> 50% of blood glucose


Bacterial meningitis

Leukocytes (usually PMNs), often greatly increased


< 50% of blood glucose (may be extremely low)

Gram staining (yield is high if 105 colony-forming units of bacteria/mL are present)

Bacterial culture

PCR or multiplex PCR panel if available

Viral meningitis

Lymphocytes (may be mixed; PMNs and lymphocytes during the first 24–48 hours)


Usually normal

Multiplex PCR panel or conventional PCR (to check for enteroviruses or herpes simplex, herpes zoster, or West Nile virus)

IgM (to check for West Nile virus or other arboviruses)

Tuberculous meningitis‡

PMNs and lymphocytes (usually mixed pleocytosis)


< 50% of blood glucose (may be extremely low)

Acid-fast staining


Mycobacterial culture (ideally using a CSF sample of ≥ 30 mL)

Interferon-gamma tests of serum and (if available) CSF

Xpert MTB/RIF§

Fungal meningitis

Usually lymphocytes


< 50% of blood glucose (may be extremely low)

Cryptococcal antigen test

Multiplex PCR panel if available (an adjunctive test, not to replace other tests)

Serologic tests for Coccidioides immitis or Histoplasma species antigen, especially if patients have recently spent time in an endemic area

Fungal culture (ideally using a CSF sample of ≥ 30 mL)

India ink (for Cryptococcus sp)

* Changes in cell count, glucose, and protein may be minimal in severely immunocompromised patients.

† In tuberculous meningitis, CSF acid-fast staining can be insensitive, sensitivity of PCR is only about 50%, and culture requires up to 8 weeks. Positive CSF interferon-gamma tests indicate tuberculous meningitis, but serum interferon-gamma tests may only indicate prior infection. Thus, confirming a diagnosis of tuberculous meningitis is difficult, and if it is strongly suspected, even if not confirmed, it is treated presumptively.

‡ A small number of cells may be present normally in neonates or after a seizure.

§ Xpert MTB/RIF (an automated rapid nucleic acid amplification test) may be used to detect M. tuberculosis DNA in CSF.

CSF = cerebrospinal fluid; PCR = polymerase chain reaction; PMNs = polymorphonuclear neutrophils.