Centor Score Calculator — Strep Pharyngitis Probability

How to Use This Calculator

1. Select Yes/No for each of the four clinical criteria (tonsillar exudates, tender nodes, fever, absence of cough).
2. Select the patient age group for the McIsaac age adjustment.
3. Score, strep probability, and recommendation display instantly.
4. Use the Strep Probability tab to look up probability for any score.
5. If a rapid strep test is available, enter the result in the Professional tier for integrated guidance.

Formula

Example

Frequently Asked Questions

• What is the Centor score and what does it assess? ▼
  The Centor score is a clinical decision rule developed by Robert Centor in 1981 to estimate the probability of group A beta-haemolytic streptococcal (GAS) pharyngitis in adults with a sore throat. The original score uses four criteria: tonsillar exudates or swelling, tender anterior cervical lymphadenopathy, temperature above 38°C or history of fever, and absence of cough — each worth 1 point. The Modified Centor score (also called the McIsaac score), published by Warren McIsaac in 1998, added an age adjustment: patients aged 3–14 receive +1 point, those 15–44 receive 0, and those 45 or older receive -1. This gives a range of -1 to 5. The score estimates GAS pharyngitis probability from approximately 1–2% at a score of 0 or below to 51–53% at a score of 4 or 5, guiding decisions about rapid antigen testing and antibiotic prescribing.
• When should antibiotics be prescribed based on the Centor score? ▼
  Antibiotic prescribing recommendations vary slightly between guidelines. The Infectious Diseases Society of America (IDSA) recommends: scores of 0–1, no testing or treatment needed; scores of 2–3, perform rapid antigen detection test (RADT) and treat only if positive; scores of 4–5, empiric antibiotic treatment is reasonable, but confirmation with RADT or culture is still preferred. NICE guidelines in the UK advise against routine antibiotics for most sore throats and recommend using the Centor or FeverPAIN score to guide a no-antibiotic, delayed-prescription, or immediate-prescription strategy. Penicillin V or amoxicillin for 10 days remains the first-line treatment for confirmed GAS pharyngitis. Antibiotic stewardship is paramount — overtreatment contributes to antimicrobial resistance.
• What are the typical complications of untreated strep pharyngitis? ▼
  Untreated GAS pharyngitis can cause suppurative (pus-forming) and non-suppurative complications. Suppurative complications include peritonsillar abscess (quinsy), retropharyngeal abscess, otitis media, sinusitis, and mastoiditis. Non-suppurative complications include acute rheumatic fever — a potentially serious sequela causing cardiac valve damage — and post-streptococcal glomerulonephritis. In developed countries, rheumatic fever has become rare (prevalence below 0.3% of GAS pharyngitis cases), largely due to improved antibiotic availability. However, in endemic regions of sub-Saharan Africa, South Asia, and parts of Latin America, rheumatic heart disease remains a major cause of cardiovascular morbidity. Antibiotics reduce suppurative complications by approximately 50% and rheumatic fever risk by over 60% when given within 9 days of symptom onset.
• How accurate is the Modified Centor score? ▼
  The Modified Centor (McIsaac) score has moderate predictive accuracy for GAS pharyngitis. A score of 4 or 5 still correctly identifies GAS in only about 50–53% of patients, meaning that even at the highest scores, close to half of patients treated empirically do not have GAS. At a score of 0 or 1, GAS prevalence is only 1–10%, making it safe to withhold antibiotics. The AUROC of the Modified Centor score in validation studies is typically 0.67–0.75, which is modest. Combining the score with rapid antigen testing (sensitivity approximately 90%, specificity approximately 97%) significantly improves accuracy. The score performs best in adults with classic presentations and is less reliable in children under 3 (where viral pharyngitis overwhelmingly predominates), immunocompromised patients, and those with prior antibiotic use.
• What is the difference between the Centor score and FeverPAIN? ▼
  Both Centor/McIsaac and FeverPAIN are clinical scores for sore throat assessment, but they differ in derivation and scope. The Centor score was derived in US emergency departments in adults, while FeverPAIN was derived in UK primary care including both adults and children. FeverPAIN uses five criteria: Fever in the past 24 hours, Purulence (pus on tonsils), Attend within 3 days, Inflamed tonsils, and No cough/coryza — totalling 0–5 points. A 2013 BMJ comparison (Little et al.) found FeverPAIN slightly outperformed Centor/McIsaac in the UK primary care context. NICE guidance recommends either score. FeverPAIN has the advantage of explicitly incorporating symptom duration (attending within 3 days), which reflects that early presentations are more likely to be bacterial.

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