Cerebrospinal Fluid Cell Count Guidelines

Normal CSF Parameters

The American College of Critical Care Medicine and Infectious Diseases Society of America establish that in immunologically normal hosts, the presence of ≤5 white blood cells/µL, normal opening pressure, and normal CSF protein concentration essentially exclude meningitis 1
In healthy adults, normal CSF contains ≤5 white blood cells per microliter (µL), with essentially no red blood cells present 1
White blood cells (WBCs) should be ≤5 cells/µL in healthy adults 1
Red blood cells (RBCs) should be essentially 0 cells/µL in non-traumatic taps 1
The CSF:plasma glucose ratio should be approximately 2/3 (or 0.6-0.7) of plasma glucose 2, 3, 4
Protein levels should be variable by age, but generally <0.6 g/L suggests against bacterial meningitis 2

Bacterial meningitis can present with normal or minimal CSF pleocytosis, particularly in early disease or immunocompromised patients 2
10% of bacterial meningitis patients had fewer than 100 cells per mm³ 2, 3, 4, 5

When traumatic tap occurs, subtract 1 WBC for every 700 RBCs present in CSF 6
Alternative formula: True CSF WBC = Actual CSF WBC - [(WBC in blood × RBC in CSF) / RBC in blood] [6]
If corrected WBC count exceeds 10 times the predicted contamination, this strongly suggests true meningitis 6
CSF lactate >35 mg/dL has 93% sensitivity and 96% specificity for bacterial meningitis 6

Maintain high suspicion for infection regardless of cell count until cultures are final in critically ill immunocompromised patients 1
Normal CSF parameters do not reliably exclude infection in immunocompromised patients 1
Additional testing (HSV PCR, CMV, fungal studies) may be required in immunocompromised patients 1

In HSV encephalitis, 5-10% of adults may have completely normal initial CSF findings with no pleocytosis, according to the Infectious Diseases Society of America 7

When blood contamination occurs during lumbar puncture, subtract 1 WBC for every 700-7000 RBCs present in CSF, as recommended by the Journal of Infection 7
Subtract 0.1 g/dL protein for every 100 red blood cells, as suggested by the Journal of Infection 7

Viral CNS infections typically produce a lymphocytic pleocytosis with tens to hundreds of cells × 10⁶/L, according to the Journal of Infection 7
Bacterial infections can mimic viral patterns, particularly tuberculosis, listeriosis, brucellosis, and partially treated acute bacterial meningitis, as noted by the Journal of Infection 7

In adults with proven HSV encephalitis, 5-10% have completely normal initial CSF findings with no pleocytosis and negative HSV PCR, and acellular CSF occurs with VZV, EBV, and CMV, particularly in immunocompromised patients 8
A second CSF examination at 24-48 hours in patients with suspected HSV encephalitis is likely to be abnormal with a positive HSV PCR if the first CSF is normal 8

When blood contamination occurs during lumbar puncture, subtract 1 WBC for every 700-7000 RBCs present in CSF, and subtract 0.1 g/dL protein for every 100 red blood cells 8