Table 2:
Comparison between normal cerebrospinal fluid and the cerebrospinal fluid seen in meningitis with different causes, and the possible reasons for delays in diagnosis*
| Characteristic | Normal CSF | Bacterial meningitis | Tuberculous meningitis | Listeria or fungal meningitis (cryptococcal) | Viral meningitis, rickettsial meningitis, fungal meningitis (cryptococcal), leptospirosis, brucellosis or syphilis |
|---|---|---|---|---|---|
| Appearance | Crystal clear | Crystal clear or cloudy | Crystal clear | Crystal clear | Crystal clear |
| Protein, g/L | < 0.4 | > 0.5 | > 0.5 | > 0.5 | < 1.5 |
| Ratio of CSF glucose level to serum glucose level | > 0.6 | < 0.5 | < 0.5 | < 0.5 | > 0.6 |
| Leukocyte count, × 106 cells/L | < 10 | > 10 | 10–500 | > 10 | > 10 |
| Predominant cell type | Mononuclear | Polynuclear (> 50%) | Lymphocytes (> 50%) | Lymphocytes (> 50%); Listeria meningitis may show a mixture of polynuclear and mononuclear cells | Lymphocytes (> 50%) |
| Gram stain | Negative | May be negative (sensitivity is 75% in Neisseria meningitis) | Rarely positive | May be negative (sensitivity in Listeria meningitis: 30%) | Negative in viral meningitis; may be negative in the other types |
| Culture | Negative | May be negative | Positive in 3–6 wk | May be negative | May be negative |
| Reason for possible delay in diagnosis | CSF findings can be normal in bacterial meningitis if the lumbar puncture is done early; Gram stain and CSF culture may be negative in Neisseria meningitis; Gram stain and culture may be negative with intercurrent use of antibiotics in all forms of bacterial meningitis | Gram stain is rarely positive; culture could be slow growing | For Listeria meningitis, Gram stain and culture may be negative (especially with intercurrent use of antibiotics); CSF leukocyte count may be normal | For Borrelia, Leptospira and Brucella, Gram stain and culture may be negative (especially with intercurrent use of antibiotics) |