Typical CSF Picture in Meningitis
The typical cerebrospinal fluid (CSF) picture in bacterial meningitis includes pleocytosis with predominantly polymorphonuclear leukocytes, low glucose concentration (typically 35 mg/dL), low CSF-to-blood glucose ratio (0.23), elevated protein levels (around 220 mg/dL), and elevated white blood cell count (approximately 2,000 cells/μL with 1,180 neutrophils/μL). 1
Bacterial Meningitis CSF Characteristics
- CSF typically shows pleocytosis with predominantly polymorphonuclear leukocytes 1
- CSF glucose is markedly decreased, with typical values around 35 mg/dL 1
- CSF-to-blood glucose ratio is typically low, around 0.23 1
- CSF protein is elevated, with concentrations around 220 mg/dL 1
- White blood cell count is elevated, typically around 2,000 cells/μL with neutrophil predominance (approximately 1,180 neutrophils/μL) 1
- CSF lactate is often elevated (>3.5 mmol/L) and has better diagnostic accuracy than CSF white blood cell count in differentiating bacterial from other types of meningitis 1, 2
Variations by Pathogen
- Streptococcus pneumoniae meningitis typically presents with more pronounced CSF abnormalities 1
- Listeria monocytogenes meningitis may not show typical CSF abnormalities in up to 26% of cases 1
- In pneumococcal meningitis, only 5% of patients have CSF WBC counts <10 cells/mm³, and 17% have less than 100 cells/mm³ 1
Special Populations
- In neonates with bacterial meningitis, CSF abnormalities may be absent in up to 6% of cases 1
- In a large cohort of neonates with culture-proven meningitis, 10% had fewer than 3 WBC/mm³ in the CSF 1
- For neonates with culture-proven meningitis, CSF WBC counts >21 cells/mm³ had a sensitivity of 79% and specificity of 81% 1
- In immunocompromised patients, normal CSF parameters do not rule out meningitis, and a high index of suspicion should be maintained until cultures are final 1
Diagnostic Value
- The CSF leukocyte count is the best diagnostic parameter for differentiating bacterial meningitis from other diagnoses, with an area under the curve of 0.95 in receiver operating characteristic analysis 1
- In immunologically normal hosts, the presence of normal opening pressure, <5 white blood cells/μL, and normal CSF protein concentration essentially excludes meningitis 1
- CSF lactate measurement has superior diagnostic value compared to other parameters, with higher sensitivity (91% vs. 41%) and negative predictive value (98% vs. 89%) compared to cell count alone 3, 2
Tuberculous Meningitis Comparison
- Unlike bacterial meningitis, tuberculous meningitis typically shows lymphocytic pleocytosis rather than neutrophilic predominance (except early in the disease) 4
- CSF in tuberculous meningitis is usually clear or cloudy, compared to the turbid appearance in bacterial meningitis 4
- Both bacterial and tuberculous meningitis show elevated protein and decreased glucose, but the pattern of cellular response differs 4
Viral Meningitis Comparison
- Viral meningitis typically shows lymphocytic pleocytosis rather than neutrophilic predominance 4
- CSF glucose is normal or only slightly decreased in viral meningitis, compared to markedly decreased in bacterial meningitis 4
- CSF protein is only mildly elevated in viral meningitis compared to markedly elevated in bacterial meningitis 4
Clinical Pearls and Pitfalls
- Prior antibiotic treatment may modify CSF findings, though one study suggested CSF WBC count may not be greatly affected by antibiotics given before lumbar puncture 1
- If bacterial meningitis is suspected and lumbar puncture is delayed for any reason (such as obtaining imaging), empirical antibiotic therapy should be started immediately after blood cultures are obtained 1
- A diagnostic algorithm comprising cell count, lactate, and PC ae C44:6 (a phosphatidylcholine) has shown 97% sensitivity and 99% negative predictive value for bacterial meningitis 3
- No single CSF test is fully reliable in distinguishing bacterial meningitis from other forms of meningitis, and results should be interpreted in the clinical context 4, 2