Cells, protein, glucose and appearance distinguish the meningitides
Expansion
| Normal | Bacterial | Viral | Tuberculous or fungal | |
|---|---|---|---|---|
| Appearance | Clear | Turbid | Clear | Clear or fibrin web |
| White cells | Under 5 | Hundreds to thousands, neutrophils | Tens to hundreds, lymphocytes | Tens to hundreds, lymphocytes |
| Protein | Under 0.45 g/l | High, over 1 | Normal or mildly raised | Very high |
| Glucose | Over 60 per cent of plasma | Low | Normal | Low |
| Opening pressure | 10 to 20 cmH2O | Raised | Normal or mildly raised | Raised |
Always send a paired plasma glucose, since the CSF value is meaningless without it.
Xanthochromia for subarachnoid haemorrhage: a yellow discolouration from bilirubin formed by the breakdown of red cells in vivo. It requires at least 12 hours after the ictus, must be protected from light, and is analysed by spectrophotometry. It distinguishes true haemorrhage from a traumatic tap, in which the red cell count falls between successive bottles and no xanthochromia develops.
Other patterns
- Guillain-Barré: albuminocytological dissociation, a raised protein with a normal cell count, typically after the first week
- Multiple sclerosis: oligoclonal bands present in CSF and absent in serum
- Fungal: India ink or cryptococcal antigen for Cryptococcus
- Partially treated bacterial meningitis can mimic a viral picture, which is why prior antibiotics must be recorded
Contraindications to lumbar puncture: signs of raised intracranial pressure or a focal mass, reduced or fluctuating consciousness, focal neurology, seizures, coagulopathy, platelets under 50, and local sepsis. Antibiotics must never be delayed to obtain the sample.