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.