Normal Cerebrospinal Fluid Cell Count in Adults
In healthy adults, normal CSF contains ≤5 white blood cells per microliter (µL) with essentially no red blood cells present. 1
Standard Normal Values
The following parameters define normal CSF in immunologically normal adults:
- White blood cells (WBCs): ≤5 cells/µL 1
- Red blood cells (RBCs): Essentially 0 cells/µL in non-traumatic taps 1
- CSF:plasma glucose ratio: Approximately 0.6-0.7 (or 2/3 of plasma glucose) 1
- Protein: Generally <0.6 g/L 1
- Opening pressure: Normal 1
The American College of Critical Care Medicine and Infectious Diseases Society of America establish that the presence of ≤5 white blood cells/µL, normal opening pressure, and normal CSF protein concentration essentially exclude meningitis in immunologically normal hosts. 1
Critical Clinical Caveats
Normal CSF parameters do not reliably exclude serious pathology in certain populations. Several important exceptions exist:
Early or Atypical Infections
- HSV encephalitis: 5-10% of adults with proven HSV encephalitis have completely normal initial CSF findings with no pleocytosis and negative HSV PCR 2, 1
- Bacterial meningitis: 10% of bacterial meningitis patients present with fewer than 100 cells per mm³ 1
- Viral encephalitis: Acellular CSF occurs with VZV, EBV, and CMV, particularly in immunocompromised patients 2
Immunocompromised Patients
- Normal CSF parameters do not reliably exclude infection in immunocompromised patients 1
- Maintain high suspicion for infection regardless of cell count until cultures are final 1
- Additional testing (HSV PCR, CMV, fungal studies) may be required 1
Timing Considerations
If the first CSF is normal in patients with suspected HSV encephalitis, a second CSF examination at 24-48 hours is likely to be abnormal with a positive HSV PCR. 2
Correction for Traumatic Tap
When blood contamination occurs during lumbar puncture, apply these corrections:
- White cells: Subtract 1 WBC for every 700-7000 RBCs present in CSF 2, 1
- Protein: Subtract 0.1 g/dL protein for every 100 red blood cells 2, 1
- Alternative formula: True CSF WBC = Actual CSF WBC - [(WBC in blood × RBC in CSF) / RBC in blood] 1
If corrected WBC count exceeds 10 times the predicted contamination, this strongly suggests true meningitis. 1
Diagnostic Reliability Range
The critical limitation of automated devices is their lower detection limit of approximately 20 cells/µL. 3 Since the clinically critical range for decision-making is 5-30 cells/µL, cell numbers <30/µL require manual confirmation by microscopy. 3 This means the normal range of ≤5 cells/µL falls below reliable automated detection, necessitating manual counting chamber methods for definitive assessment. 3