Centor / McIsaac Score Calculator (Strep Throat)

The Centor score, modified by McIsaac, estimates how likely a sore throat is caused by Group A Streptococcus(GAS) rather than a virus. It is a bedside decision aid designed to reduce unnecessary antibiotics: most acute pharyngitis is viral and needs no antibiotic at all. The score is purely additive — you add up points for a patient's age and four clinical findings, with no other arithmetic.

Robert Centor described the original four criteria in 1981. Each is worth one point when present:

• Temperature > 38 °C (or a history of fever) → 1
• Tonsillar exudate or swelling → 1
• Tender / swollen anterior cervical lymph nodes → 1
• Absence of cough → 1

Warren McIsaac and colleagues added an age adjustment in 1998, because GAS is common in children and rare in older adults:

• Age 3–14 → +1
• Age 15–44 → 0
• Age 45 or older → −1

The modified total is score = fever + exudate + nodes + no-cough + age adjustment, which ranges from −1 (an older adult with no criteria) to 5 (a child aged 3–14 with all four). The tool also shows the classic Centor score — the four criteria without the age point — so you can see how age changes the picture.

Each total maps to an estimated GAS probability from the McIsaac 2004 (JAMA validation cohort): about 1–2.5% at −1 or 0, 5–10% at 1, 11–17% at 2, 28–35% at 3, and 51–53% at 4 or 5. These are quoted as ranges, not false-precision point estimates. The management steps follow IDSA 2012 (Clin Infect Dis): a score of 0–1 needs no testing or antibiotics; 2–3 warrants a rapid antigen detection test (RADT) or throat culture with treatment only if positive; and at 4 or more some guidelines allow empiric treatment while the test is pending. IDSA is explicit that adults should not receive empiric antibiotics without a positive test — the score guides testing, not reflex prescribing.

• McIsaac WJ, et al. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ 1998;158(1):75–83 (the age-adjusted modification and point scheme)
• McIsaac WJ, et al. Empirical validation of guidelines for the management of pharyngitis in children and adults. JAMA 2004;291(13):1587–1595 (observed GAS probability by score)
• Shulman ST, et al. (IDSA) Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update. Clin Infect Dis 2012;55(10):e86–e102 (testing/treatment recommendations)

The criteria, age adjustment, GAS probabilities and management bands on this page were last cross-checked against these sources on 2026-07-15(Centor 1981 / McIsaac 1998 (CMAJ)). This tool is for education and reference only; it aids, but does not replace, assessment by a qualified clinician, and it does not apply to red-flag presentations such as a suspected peritonsillar abscess or airway compromise.