Scores & indices

Centor score calculator

Q: How does age change the score?

The McIsaac modification: age 3–14 adds 1 point, age 15–44 adds nothing (leave both age items unticked), and age 45 or over subtracts 1 — reflecting how strongly strep prevalence falls with age.

Q: What is the strep probability at each score?

Approximately, from the McIsaac derivation and validation cohorts: around 2–6% at 0–1, ~15% at 2, ~32% at 3, and ~52% at 4–5 — roughly a coin flip at the top, and a few percent at the bottom.

Q: Who should get antibiotics for a sore throat?

At 0–1, no test and no antibiotics. At 2–3, test with rapid antigen or culture and treat only if positive. At 4–5 some policies allow empiric treatment where testing is unavailable. Most sore throats are viral.

Q: Why does treating strep throat matter in South Africa?

Antibiotics shorten symptoms and reduce suppurative complications, but the key benefit where acute rheumatic fever is endemic — as in South Africa — is ARF prevention, which is why a lower threshold for testing and treating children is deliberate local policy.

Four signs and an age band settle the sore-throat question — reassure, swab, or treat — with rheumatic fever prevention in view.

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Age: 3–14 adds 1 · 15–44 adds 0 (leave both age items unticked) · ≥ 45 subtracts 1.Antibiotics shorten symptoms, reduce suppurative complications, and prevent acute rheumatic fever — the key benefit where ARF is endemic, as in South Africa. Most sore throats are viral.References: Centor 1981; McIsaac, CMAJ 1998; McIsaac, JAMA 2004 (validation).

How to read the result

Centor (McIsaac) falls into these published bands.

< 2Low — no test, no antibiotics

2 – 3TestRADT or throat culture; treat only if positive.

≥ 4Test ± empiric per policyProbability ~50% — some policies allow empiric treatment where testing is unavailable.

Worked example

A 9-year-old with tonsillar exudate and tender anterior cervical nodes — no fever recorded, and a cough is present.

Centor (McIsaac) 3 — test: streptococcal probability ~32%

Squarely in the testing band: rapid antigen test or throat culture, and antibiotics only if positive. In a child in an ARF-endemic setting, confirming and treating strep is exactly the case the score exists for.

Who this is for

For clinicians facing the everyday sore throat in primary care, emergency centres, and paediatric clinics. Tonsillar exudate, tender anterior cervical nodes, fever over 38 °C, and absence of cough each score a point, with McIsaac's age modification on top — separating the mostly viral majority from the throats worth testing. In South Africa the calculus includes preventing acute rheumatic fever, which deliberately lowers the threshold for testing and treating children.

How it works

What it calculates

The probability that a sore throat is group-A streptococcal, from the four Centor criteria plus the McIsaac age modification.

Interpreting the result

0–1: a few percent — no test, no antibiotics. 2–3: test (rapid antigen or culture) and treat only if positive. 4–5: roughly a coin flip — test where available; some policies allow empiric treatment where it is not.

The South African context

Where acute rheumatic fever is endemic, preventing it is the principal reason to treat streptococcal pharyngitis — a lower threshold for testing and treating children is deliberate local policy. References: Centor 1981; McIsaac 1998, 2004.

Built on published evidence

Centor 1981; McIsaac, CMAJ 1998; McIsaac, JAMA 2004 (validation)

Codification last reviewed 2026-08-28, and checked against published reference values in automated tests on every release — see the full evidence ledger.

Questions clinicians ask

How does age change the score?

The McIsaac modification: age 3–14 adds 1 point, age 15–44 adds nothing (leave both age items unticked), and age 45 or over subtracts 1 — reflecting how strongly strep prevalence falls with age.

What is the strep probability at each score?

Approximately, from the McIsaac derivation and validation cohorts: around 2–6% at 0–1, ~15% at 2, ~32% at 3, and ~52% at 4–5 — roughly a coin flip at the top, and a few percent at the bottom.

Who should get antibiotics for a sore throat?

At 0–1, no test and no antibiotics. At 2–3, test with rapid antigen or culture and treat only if positive. At 4–5 some policies allow empiric treatment where testing is unavailable. Most sore throats are viral.

Why does treating strep throat matter in South Africa?

Antibiotics shorten symptoms and reduce suppurative complications, but the key benefit where acute rheumatic fever is endemic — as in South Africa — is ARF prevention, which is why a lower threshold for testing and treating children is deliberate local policy.

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