What are the normal cerebrospinal fluid (CSF) values for a healthy adult?

Normal Cerebrospinal Fluid Values in Adults

In healthy adults, normal CSF contains ≤5 white blood cells/µL, essentially 0 red blood cells, protein <0.4-0.6 g/L, a CSF:plasma glucose ratio of 0.6-0.7, glucose 2.6-4.5 mmol/L, and opening pressure of 12-20 cm H₂O (120-200 mm H₂O). 1

Core CSF Parameters

Cellular Components

• White blood cells (WBCs): ≤5 cells/µL is the established normal upper limit 1, 2
• Red blood cells (RBCs): Essentially 0 cells/µL in non-traumatic lumbar punctures 1, 2
• Differential: Predominantly lymphocytes in normal CSF 3

Biochemical Parameters

• Protein: <0.4-0.6 g/L (40-60 mg/dL), with albumin CSF/serum ratio (Qalb) preferred over total protein measurement 1, 3
• Glucose: 2.6-4.5 mmol/L (approximately 45-80 mg/dL) 1
• CSF:plasma glucose ratio: 0.6-0.7 (approximately 2/3 of plasma glucose) 1, 2
• Lactate: <2 mmol/L (<35 mg/dL) 1

Physical Characteristics

• Appearance: Clear and transparent 1, 4
• Opening pressure: 12-20 cm H₂O (120-200 mm H₂O) 1

Critical Clinical Caveats

Age-Related Variations

• Protein levels increase with age: Normal upper limits for Qalb should be adjusted based on patient age 3
• Neonates have significantly different values: Higher WBC counts (up to 12 cells/µL in preterm, 10 cells/µL in term) and protein concentrations (up to 210 mg/dL in preterm, 110 mg/dL in term) are normal in the first months of life 1, 5

Traumatic Tap Corrections

When blood contamination occurs during lumbar puncture, apply these correction formulas:

• WBC correction: Subtract 1 WBC for every 700 RBCs present in CSF 2
• Alternative WBC formula: True CSF WBC = Actual CSF WBC - [(Blood WBC × CSF RBC) / Blood RBC] 1, 2
• Protein correction: Subtract 0.1 g/dL (10 mg/dL) for every 100 RBCs 1, 2

Diagnostic Pitfalls to Avoid

Do not rely solely on normal CSF parameters to exclude serious infections. Several critical scenarios can present with deceptively normal CSF:

• Bacterial meningitis: 10% of patients have <100 cells/mm³, and some present with normal or minimal pleocytosis, particularly in early disease or immunocompromised patients 1, 2
• HSV encephalitis: 5-10% of adults have completely normal initial CSF findings with no pleocytosis and negative HSV PCR 2
• Immunocompromised patients: Maintain high suspicion for infection regardless of cell count until cultures are final 6, 2

When Normal Values Essentially Exclude Meningitis

In immunologically normal hosts, the combination of ≤5 WBCs/µL, normal opening pressure, and normal CSF protein concentration essentially excludes meningitis 6, 2

Additional Diagnostic Markers

• CSF lactate >35 mg/dL (>4.0 mmol/L): Has 93% sensitivity and 96% specificity for bacterial meningitis, particularly useful in postoperative neurosurgical patients 6, 1
• Intrathecal immunoglobulin synthesis: Best demonstrated by isoelectric focusing for chronic inflammatory conditions 3