Normal Lymphocyte Level in CSF
In healthy adults, normal CSF contains ≤5 white blood cells per microliter (µL), with lymphocytes comprising the predominant cell type among these few cells. 1
Normal CSF White Blood Cell Parameters
The established threshold for normal CSF cellularity is straightforward:
- Total white blood cells should be ≤5 cells/µL in healthy adults 1
- Red blood cells should be essentially 0 cells/µL in non-traumatic lumbar punctures 1
- The American College of Critical Care Medicine and Infectious Diseases Society of America confirm that ≤5 white blood cells/µL in immunologically normal hosts essentially excludes meningitis 1
Lymphocyte Predominance in Normal CSF
While the guidelines specify total WBC counts rather than specific lymphocyte percentages, lymphocytes are the predominant cell type in normal CSF:
- In normal CSF with low cell counts, T lymphocytes constitute the majority of white cells present 2, 3
- Flow cytometric studies demonstrate that even in samples with as few as 1 leukocyte per 3 µL, T lymphocytes can be reliably identified 2
- Blood-to-CSF ratios for total T cells (CD3+) are approximately 2000:1, indicating selective barrier properties that favor T lymphocyte transfer 3
Critical Clinical Caveats
Do not assume infection is absent based solely on cell count in certain populations:
- Bacterial meningitis can present with normal or minimal CSF pleocytosis, particularly in early disease or immunocompromised patients 1
- Approximately 10% of bacterial meningitis patients had fewer than 100 cells per mm³ 1
- In HSV encephalitis, 5-10% of adults may have completely normal initial CSF findings with no pleocytosis 4
- Normal CSF parameters do not reliably exclude infection in immunocompromised patients 1
Correcting for Traumatic Tap
When blood contamination occurs during lumbar puncture, adjust the white cell count:
- Subtract 1 WBC for every 700-7000 RBCs present in CSF (guidelines vary: 1 uses 700, 4 uses 7000) 4, 1
- Alternative formula: True CSF WBC = Actual CSF WBC - [(WBC in blood × RBC in CSF) / RBC in blood] 1
- Subtract 0.1 g/dL protein for every 100 red blood cells 4
Lymphocytic Pleocytosis Patterns
When CSF shows elevated lymphocytes (>5 cells/µL), consider the differential:
- Viral CNS infections typically produce a lymphocytic pleocytosis with tens to hundreds of cells × 10⁶/L 4
- Bacterial infections can mimic viral patterns, particularly tuberculosis, listeriosis, brucellosis, and partially treated acute bacterial meningitis 4
- Mild to moderate pleocytosis (even ≥10 cells/µL) does not exclude chronic inflammatory conditions like CIDP, especially with subacute onset 5