II. Interpretation: Normal Findings
- No Polymorphonuclear Lymphocytes (Neutrophils)
- Normal CSF may have 1-2 PMNs present
- Adults: 5 or less WBC/mm3
- Newborns: 20 or less WBC/mm3
III. Interpretation: Correction of WBCs for CSF RBC
- Adults
- One WBC for every 500-1500 CSF RBCs
- WBCpredicted = RBCcsf x (WBCblood/RBCblood)
- Infants
- One WBC for every 1000 CSF RBCs
- Lyons (2017) Ann Emerg Med 69(5): 622-31 [PubMed]
IV. Interpretation: Cell Differential
- Differential does not distinguish Bacterial from viral
- Lymphocyte predominance in 10% Bacterial Meningitis
- Monocytes (Up to 50 cells/mm3)
-
Eosinophils
- Intracranial Parasite infection
- Aseptic Meningitis
- Malignancy
- Ventriculoperitoneal Shunt
V. Interpretation: Pleocytosis (WBCs in CSF) Causes
-
Bacterial Meningitis
- PMNs predominate
- CSF WBCs >100/mm3 in 99% of cases (>1000 for most)
-
Viral Meningitis
- Lymphocytes predominate
- CSF WBCs usually <100/mm3
- Chronic intracranial inflammation (Lymphocytes)
- Subarachnoid Hemorrhage
- Thrombosis
- Infectious Mononucleosis
- CNS Parasitic Infection (Eosinophils predominate)
- Carcinomatous Meningitis (<100 cells)
VI. Interpretation: Examination pointers
- Acetic acid lyses CSF RBCs but leaves CSF WBCs intact
- Methylene blue distinguishes PMNs and Lymphocytes
VII. References
- Kooiker in Roberts (1998) Procedures in ER, p. 1067-75
- Ravel (1995) Lab Medicine, Mosby, p. 294-9
- Tunkel in Mandell (2000) Infectious Disease, p. 974-8
- Seehusen (2003) Am Fam Physician 68:1103-8 [PubMed]