CSF Analysis and Meningitis Management Guidelines

Diagnostic Procedures

The American College of Physicians recommends collecting at least 22 mL of CSF from adults for comprehensive diagnostic testing, as CSF is produced at approximately 15 mL/hour and this volume can be safely removed 1, 2
The first 2-2.5 mL of CSF should be allocated for cell count with differential, microscopy, culture, and sensitivities, with a minimum of 5 mL optimal for standard diagnostic procedures 2
Additional volume requirements include 2 mL for viral studies 2, 6 mL for tuberculous meningitis 2, and 1-2 mL for protein and glucose measurements 2

The Infectious Diseases Society of America recommends performing cell count with differential 3, 1, glucose concentration with concurrent plasma glucose 3, 1, protein concentration 3, 1, opening pressure (unless performed in sitting position) 1, Gram stain (sensitivity 50-99%, specificity 97-100%) 4, 5, and bacterial culture (diagnostic in 70-85% of untreated cases) 4, 5
CSF PCR should be performed, especially if antibiotics were given prior to lumbar puncture, as it has sensitivity of 87-100% and specificity of 98-100% 4, 6, 5

In bacterial meningitis, critical findings include elevated opening pressure (>20 cm CSF) 1, 6, 5, turbid, cloudy, or purulent appearance 4, 6, 5, WBC count typically >100 cells/μL (often >2,000/μL) 3, 4, 6, 5, and predominant cell type of neutrophils 4, 6, 5
In viral meningitis, critical findings include normal or mildly raised opening pressure 4, 6, 5, clear appearance 4, 6, 5, WBC count typically 5-1,000 cells/μL 4, 6, 5, and predominant cell type of lymphocytes (may be neutrophils early in enteroviral disease) 4, 6, 5

In febrile patients with ventriculostomy or VP shunt, obtain CSF from the reservoir; if CSF flow is obstructed, also obtain lumbar CSF as one space may be infected while the other is sterile 3
Remove ventriculostomy catheters in patients who develop stupor or meningitis signs and culture the tip 3

Normal opening pressure, <5 WBC/μL, and normal CSF protein essentially exclude meningitis in immunologically normal hosts 3, 7

If bacterial meningitis is suspected and lumbar puncture is delayed for any reason, start empirical antibiotic therapy immediately after obtaining blood cultures—do not wait for CSF results 3, 7

In healthy adults, cerebrospinal fluid (CSF) contains ≤ 5 white blood cells (WBC)/µL, essentially no red blood cells in a non‑traumatic tap, a CSF/plasma glucose ratio of 0.6–0.7, and protein < 0.6 g/L; opening pressure is typically 12–20 cm H₂O. 8

CSF is usually turbid or purulent, with opening pressure > 20 cm H₂O, WBC count often > 100 cells/µL (frequently > 2,000 cells/µL) and a neutrophil predominance. 8
Protein is markedly elevated; values < 0.6 g/L make bacterial meningitis unlikely. 8
Glucose is very low; a CSF/plasma glucose ratio < 0.36 provides 93 % sensitivity and specificity for bacterial meningitis (high‑level evidence). 8
CSF lactate > 35 mg/dL yields 93 % sensitivity and 96 % specificity for bacterial meningitis when antibiotics have not yet been administered (high‑level evidence). 8
Approximately 10 % of bacterial meningitis cases present with < 100 WBC/µL, and Listeria or partially treated infections may show a lymphocyte predominance. 8

CSF is typically clear, with opening pressure normal or mildly raised, WBC count ranging from 5 to 1,000 cells/µL and a lymphocyte predominance (early enteroviral disease may show neutrophils). 8
Protein is mildly elevated and glucose is normal or only slightly reduced. 8

CSF may be clear or cloudy, with raised opening pressure, WBC count 5–500 cells/µL (lymphocyte predominance), markedly elevated protein, and very low glucose (CSF/plasma glucose ratio also very low). 8

CSF may appear clear or cloudy, with raised opening pressure, WBC count 5–500 cells/µL (lymphocyte predominance), increased protein, and low glucose (CSF/plasma glucose ratio low). 8

Normal opening pressure, WBC < 5 cells/µL, and normal protein essentially exclude meningitis. 8
CSF glucose > 2.6 mmol/L (≈ 0.6 g/L) is unlikely to be bacterial meningitis. 8
CSF protein < 0.6 g/L argues against bacterial meningitis. 8

All statements are derived from the Journal of Infection (2016) and reflect the evidence reported therein.