Centor / McIsaac Score Calculator

The Centor score estimates how likely an acute sore throat is caused by group A streptococcus (strep throat). It awards one point each for tonsillar exudate or swelling, tender anterior cervical lymph nodes, a history of fever above 38 C (100.4 F), and the absence of cough. The McIsaac modification adds an age adjustment, which makes the score more accurate across children and adults.

Add one point for each of the four clinical criteria that is present, then apply the age adjustment: add 1 point for ages 3 to 14, add 0 for ages 15 to 44, and subtract 1 point for ages 45 and over. The total ranges from -1 to 5. For example, an adult of 30 with exudate, tender nodes, fever, and no cough scores 4, since the age adjustment is 0.

Higher scores mean a higher chance of strep. A score of 0 or less suggests roughly a 1 to 2.5% chance, a score of 1 about 5 to 10%, a score of 2 about 11 to 17%, a score of 3 about 28 to 35%, and a score of 4 or 5 about 51 to 53%. These ranges come from the McIsaac validation studies and are estimates, not a diagnosis.

For a score of 0 or 1, testing and antibiotics are generally not recommended, so symptomatic care is enough. For a score of 2 or 3, a rapid antigen strep test or throat culture is suggested, with antibiotics only if the result is positive. For a score of 4 or more, clinicians may consider empiric antibiotics or test and treat, following local guidelines.

Use it only for acute sore throat of recent onset, meaning symptoms present for 3 days or less. It is not validated for children under 3, since strep is rare at that age, and it does not apply to chronic sore throat or other causes such as mononucleosis. It is a triage aid to guide testing, not a replacement for examination.

No. This calculator is for education only and is not a substitute for professional medical advice, diagnosis, or treatment. The probabilities and management bands follow the McIsaac modification of the Centor criteria, but the actual decision to test or prescribe antibiotics must be made by a qualified clinician who has examined the patient.