Centor Score Calculator (Modified / McIsaac Strep Throat)
Likelihood of group A streptococcal pharyngitis with the modified Centor (McIsaac) score — tonsillar exudate, tender anterior nodes, fever, absence of cough, age — with rapid-test and antibiotic guidance and the FeverPAIN alternative.
How it works
Exudate 1 + tender anterior nodes 1 + fever 1 + no cough 1; age 3–14 +1, 15–44 0, ≥ 45 −1. ≤ 1 no test, 2–3 test, ≥ 4 high probability
Most sore throats are viral and antibiotics do nothing for them, yet they are among the commonest reasons antibiotics are prescribed. The Centor criteria, extended by McIsaac to adjust for age, estimate how likely a pharyngitis is due to group A streptococcus — the one common cause that benefits from penicillin, chiefly to prevent rheumatic fever and shorten symptoms by about a day. Even at the top score barely half of patients have strep, which is why most guidelines advise confirming with a rapid antigen test before treating, and skipping both test and antibiotics at scores of 0–1. The UK’s FeverPAIN score is an alternative that adds purulence, rapid attendance and severe inflammation.
Worked example
A 9-year-old with fever, exudate, tender nodes and no cough: 4 + 1 (age) = 5 — about 51–53% probability; rapid strep test and treat if positive.
Frequently asked questions
Why not just treat a high score?
Because roughly half of high scorers still have viral infections. Testing avoids needless antibiotics; some guidelines (NICE) allow empirical treatment at FeverPAIN 4–5 or Centor 3–4.
Does Centor apply to children under 3?
No — strep pharyngitis is rare under 3 and presents differently; the score was validated from age 3 upward.
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Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.