What it is
The Bacterial Meningitis Score (BMS), derived by Nigrovic and colleagues, identifies children with CSF pleocytosis who are at very low risk of bacterial (as opposed to aseptic/viral) meningitis. It is applied after the lumbar puncture shows pleocytosis, to support — not replace — decisions about admission and continued antibiotics.
The predictors
The score totals out of 6. Gram stain carries two points; the rest one each:
| Predictor | Points |
|---|---|
| Positive CSF Gram stain | +2 |
| CSF ANC ≥1000 cells/µL | +1 |
| CSF protein ≥80 mg/dL | +1 |
| Peripheral blood ANC ≥10,000 cells/µL | +1 |
| Seizure at or before presentation | +1 |
Interpretation
- Score 0 — very low risk. Negative predictive value ~99.9% for bacterial meningitis in the validation cohorts.
- Score ≥1 — not low risk. Any single positive predictor moves the child out of the low-risk band; treat as possible bacterial meningitis pending cultures.
This is a binary rule in practice: zero versus non-zero.
When to use it
In the well-appearing child >2 months with CSF pleocytosis, to help justify shorter observation or outpatient management while cultures are pending. It supports clinical reasoning in the borderline case — it does not authorise withholding antibiotics from a child you are worried about.
Worked example
A 4-year-old with fever and headache, no seizure (0). CSF: Gram stain negative (0), ANC 220 cells/µL (0), protein 45 mg/dL (0). Blood ANC 7,800 (0).
Score 0 → very low risk. Combined with a reassuring exam, this supports a viral/aseptic course — but only because every exclusion below is also clear.
Pitfalls — the exclusions matter most
The rule is NOT validated in, and must not be applied to:
- Infants <2 months
- The critically ill or toxic-appearing child
- Children pre-treated with antibiotics (Gram stain and counts are blunted)
- VP shunt, recent neurosurgery, or neurosurgical hardware
- The immunocompromised
- Purpura/petechiae or other features of invasive meningococcal disease
Other traps: a traumatic tap distorts CSF counts; the rule predicts bacterial meningitis, not other serious bacterial infection; and local guidelines and clinical judgement override the score. When any predictor is positive — or any exclusion applies — treat as possible bacterial meningitis.
Run it: Bacterial Meningitis Score (Children)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.