How this calculator works
The McIsaac modification adds an age adjustment to four one-point throat-infection predictors. The adjustment is +1 at ages 3-14, zero at 15-44 and -1 from age 45. The original 1998 study developed the age-appropriate approach in primary care. This page reports the arithmetic score only; it does not assign a fixed probability from another population or recommend antibiotics. Examination, local testing guidance and features suggesting other causes remain necessary. The result is an estimate for information only and is not medical advice.
Formula
Clinical total = fever above 38°C + tonsillar swelling/exudate + tender anterior cervical nodes + absence of cough, one point each. McIsaac score = clinical total + age adjustment. The arithmetic range is -1 to 5.
Worked example
A 10-year-old with all four findings has 4 + 1 = 5. A 50-year-old with fever and no other finding has 1 - 1 = 0.
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Frequently asked questions
Does a cough add a point?
No. The predictor is the absence of cough. Select Yes only when cough is absent.
What happens at ages 15 and 45?
Age 15 enters the zero-adjustment band; age 45 enters the minus-one band.
Does the score confirm streptococcal infection?
No. A score cannot by itself identify the organism or choose treatment. Follow the relevant clinical testing guidance.