What it is
The Centor score estimates the probability that a sore throat is caused by group A Streptococcus (GAS). McIsaac added an age adjustment, extending and validating it for patients from 3 years upward. It is a pretest-probability tool to rationalise rapid antigen detection testing (RADT), throat culture, and antibiotics — not a standalone diagnosis.
The criteria
Each feature scores +1:
| Criterion | Points |
|---|---|
| Temperature >38°C (history or measured) | +1 |
| Absence of cough | +1 |
| Tender/swollen anterior cervical nodes | +1 |
| Tonsillar swelling or exudate | +1 |
McIsaac age adjustment:
| Age | Points |
|---|---|
| 3–14 years | +1 |
| 15–44 years | 0 |
| ≥45 years | −1 |
Total ranges −1 to +5.
Interpreting the total
| Score | Approx. GAS probability | Suggested action |
|---|---|---|
| ≤0 | ~1–2.5% | No testing, no antibiotics |
| 1 | ~5–10% | No testing or RADT only |
| 2 | ~11–17% | RADT / culture; treat if positive |
| 3 | ~28–35% | RADT / culture; treat if positive |
| ≥4 | ~51–53% | RADT / culture; some treat empirically |
Why “test, don’t empirically treat”
In children and adolescents, IDSA and most national bodies recommend confirming GAS with RADT or throat culture before antibiotics, because:
- Clinical features overlap heavily with viral pharyngitis; even a score of 4 carries roughly even odds.
- Most sore throats are viral, and empiric prescribing drives antibiotic resistance and avoidable allergic/adverse events.
- A negative RADT in a child should be backed up by throat culture (RADT sensitivity ~85–90%), because untreated GAS in children carries a small risk of acute rheumatic fever — still relevant in India and other high-burden settings.
The exception is the very high-probability adult where some guidance permits empiric treatment; in children, confirm.
GAS is rare under age 3
Classic streptococcal pharyngitis and its suppurative/non-suppurative sequelae are uncommon below 3 years, and acute rheumatic fever is very rare in this group. The McIsaac validation starts at age 3, so do not apply the score — or routinely test and treat for strep — in toddlers and infants with a sore throat or coryza. Look instead for streptococcosis (protracted nasopharyngitis) or, more often, a viral cause.
Pitfalls
- A high score does not confirm GAS; a positive RADT/culture does. Carriage (positive test with viral illness) is common in children.
- Do not score patients with classic viral features (coryza, conjunctivitis, hoarseness, oral ulcers, viral exanthem) toward antibiotics — these point away from GAS regardless of the number.
- Scarlet fever, peritonsillar abscess, or systemic toxicity need their own assessment, not just a score.
Run it now: Centor / McIsaac Calculator
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.