Normal Ranges of CSF Parameters
The normal cerebrospinal fluid values are: glucose 2.6-4.5 mmol/L (47-81 mg/dL), protein <0.4 g/L, CSF/plasma glucose ratio >0.66, white blood cell count <5 cells/μL, and opening pressure 12-20 cm CSF. 1
Glucose
- Normal CSF glucose ranges from 2.6 to 4.5 mmol/L (approximately 47-81 mg/dL) 1
- CSF glucose is typically about two-thirds of the plasma glucose concentration 1
- The CSF/plasma glucose ratio should normally be >0.66 1
- CSF glucose levels are influenced by blood glucose levels up to 6 hours before lumbar puncture, so timing matters when interpreting isolated values 2
Clinical Context for Glucose Interpretation
- A CSF glucose >2.6 mmol/L makes bacterial meningitis unlikely 1
- In patients with normal glucose metabolism, the CSF/blood glucose ratio ranges from 0.35-0.95 at 0-6 hours before lumbar puncture 2
- For patients with abnormal or unclear glucose metabolism, the CSF/average blood glucose ratio (0.33-0.78) should be used rather than absolute values 2
Protein
- Normal CSF protein is <0.4 g/L 1
- Local laboratory ranges should be consulted as they may vary slightly from these quoted values 1
- A CSF protein <0.6 g/L makes bacterial meningitis unlikely 1
pH
- Normal CSF pH is not explicitly defined in the provided guidelines, as pH measurement is not routinely performed in standard CSF analysis 1
- The guidelines focus on lactate measurement rather than pH for distinguishing bacterial from viral meningitis 1
Lactate Dehydrogenase (LDH)
- Normal CSF LDH values are not standardized in the major meningitis guidelines 1
- One research study suggests a CSF LDH value of <40 U/L may be considered normal, with values ≥40 U/L showing 86.3% sensitivity for detecting bacterial meningitis 3
- A CSF/serum LDH ratio of <0.1:1.0 is generally considered normal 3
- LDH is not routinely recommended in current guidelines for CSF analysis, as lactate measurement has largely replaced it for diagnostic purposes 1
Additional Normal CSF Parameters
- White blood cell count: <5 cells/μL 1
- Opening pressure: 12-20 cm CSF (when measured in lateral recumbent position, not sitting) 1
- Appearance: Clear 1
- Predominant cell type: None (or rare lymphocytes if any cells present) 1
Important Clinical Caveats
- A traumatic lumbar puncture will falsely elevate white cells and protein due to blood contamination; a common correction factor used is 1:1000 (1 WBC per 1000 RBCs) 1
- Neonates have different normal values: term neonates may have higher CSF protein and different CSF/blood glucose ratios, with a ratio of 0.6 considered abnormal (not 0.4 as in older children and adults) 4
- CSF lactate (not LDH) has become the preferred rapid test, with normal values <2 mmol/L effectively ruling out bacterial disease 5
- When interpreting CSF glucose in isolation without simultaneous plasma glucose, values must be interpreted cautiously in the clinical context 1