Meningitis: CSF analysis
Normal CSF values
| Parameter | Normal Range | Notes |
|---|---|---|
| Opening pressure | 10–20 cmH₂O | With patient in lateral decubitus position |
| Appearance | Clear | Turbid or cloudy may indicate infection or inflammation |
| White cell count | 0–5 cells/mm³ | Lymphocytes; >5 suggests infection or inflammation |
| Red cell count | 0 cells/mm³ | Presence may indicate traumatic tap or subarachnoid haemorrhage |
| Protein | 0.15–0.45 g/L | Higher in neonates; raised in infection, inflammation, or malignancy |
| Glucose | 2.5–4.4 mmol/L or 60–80% of plasma level | Low in bacterial, TB, and fungal meningitis |
| CSF:Serum glucose ratio | >0.6 | <0.4 suggests bacterial or TB meningitis |
| Lactate | <2.0 mmol/L | Elevated in bacterial meningitis |
Normal CSF values compared to meningitis of various aetiology
| Parameter | Normal | Bacterial Meningitis | Viral Meningitis | TB Meningitis | Fungal Meningitis |
|---|---|---|---|---|---|
| Opening Pressure | 10–20 cmH₂O | >20 cmH₂O | Normal or mildly raised | >20 cmH₂O | Elevated or normal |
| Appearance | Clear | Turbid (cloudy) | Clear or slightly cloudy | Cobweb clot or slightly cloudy | Clear or slightly cloudy |
| WCC | 0–5 cells/mm³ | >1,000 cells/mm³ (predominantly neutrophils) | 10–1,000 cells/mm³ (lymphocytes) | 50–500 cells/mm³ (lymphocytes) | 20–500 cells/mm³ (lymphocytes) |
| Protein | 0.15–0.45 g/L | >1.0 g/L | Slightly raised (0.5–1.0 g/L) | >1.0 g/L | >0.5 g/L |
| Glucose | 2.5–4.4 mmol/L or >60% of plasma | <2.2 mmol/L or <40% of plasma | Normal or mildly reduced | <2.2 mmol/L | <2.2 mmol/L |
| CSF:Serum Glucose Ratio | >0.6 | <0.4 | Normal or slightly reduced | <0.4 | <0.4 |
| Gram Stain/ZN stain | Negative | Usually positive (Gram +ve/-ve organisms) | Negative | Acid-fast bacilli may be seen (ZN stain) | May show yeasts (e.g. Cryptococcus) |
| Lactate | <2.0 mmol/L | >3.5 mmol/L | Normal or slightly raised | Raised | Raised |
CSF notes
The Ziehl-Neelsen stain is only 20% sensitive in the detection of tuberculous meningitis and therefore PCR is sometimes used (sensitivity = 75%)
A low glucose may be seen in some viral causes of meningitis such as herpes encephalitis mumps
The Ziehl-Neelsen stain is only 20% sensitive in the detection of tuberculous meningitis and therefore PCR is sometimes used (sensitivity = 75%)
A low glucose may be seen in some viral causes of meningitis such as herpes encephalitis mumps