Clinical Decision-Making
Centor and McIsaac Score: Strep Throat Diagnosis and Antibiotic Stewardship
Centor score predicts GAS pharyngitis probability using 4 clinical criteria. McIsaac adds age adjustment. Score 0–1 = no testing needed; 2–3 = RADT; ≥4 = RADT or empirical treatment. Neither score should drive antibiotic prescriptions alone — RADT confirmation is the evidence-based bridge.
TL;DR: Centor score predicts Group A Streptococcal (GAS) pharyngitis probability using 4 clinical criteria: tonsillar exudates, tender anterior cervical lymphadenopathy, fever history, and absence of cough. McIsaac adds age adjustment. Score 0–1 = no testing needed (viral probability >80%); 2–3 = RADT; ≥4 = RADT or empirical treatment. Neither score should drive antibiotic prescriptions alone — RADT confirmation is the evidence-based bridge between clinical suspicion and treatment.
The Antibiotic Stewardship Problem
Pharyngitis is one of the most common reasons for primary care visits and antibiotic prescriptions globally. Only 5–15% of adult sore throats are caused by GAS. Yet studies consistently show 60–80% of pharyngitis presentations receive antibiotics.
Centor Score (Original)
| Criterion | Points |
|---|---|
| Tonsillar exudates | +1 |
| Tender anterior cervical lymphadenopathy | +1 |
| History of fever (≥38°C) | +1 |
| Absence of cough | +1 |
Score range: 0–4
McIsaac Modified Score
Adds age adjustment to Centor:
| Age Group | Modification |
|---|---|
| 3–14 years | +1 point |
| 15–44 years | 0 points |
| ≥45 years | −1 point |
Score range: −1 to 5
Score-Based Management
| McIsaac Score | GAS Probability | Recommended Action |
|---|---|---|
| ≤0 | 1–2.5% | No testing, no antibiotics |
| 1 | 5–10% | No testing (culture optional) |
| 2 | 11–17% | RADT; treat only if positive |
| 3 | 28–35% | RADT; treat only if positive |
| ≥4 | 51–53% | RADT; consider empirical treatment if RADT unavailable |
Antibiotic Choice
First-line: Penicillin V or amoxicillin × 10 days. GAS has never developed clinically meaningful penicillin resistance.
Penicillin allergy: Cephalexin (non-severe) or azithromycin/clindamycin (severe).
Evidence and Guidelines
- Kanagasabai A, et al. Clin Microbiol Infect. 2024;30(4):445–452. PMID: 38182052.
- Palla AH, et al. BMC Pulm Med. 2012;12:70. PMID: 23176084.
- Centor RM, et al. Med Decis Making. 1981;1(3):239–246. PMID: 6520418.
- McIsaac WJ, et al. CMAJ. 1998;158(1):75–83. PMID: 9475915.
- Shulman ST, et al. IDSA Guidelines. Clin Infect Dis. 2012;55(10):1279–1282. PMID: 23091044.
References
- Kanagasabai A, et al. Clin Microbiol Infect. 2024;30(4):445–452.
- Palla AH, et al. BMC Pulm Med. 2012;12:70.
- Centor RM, et al. Med Decis Making. 1981;1(3):239–246.
- McIsaac WJ, et al. CMAJ. 1998;158(1):75–83.
- Shulman ST, et al. Clin Infect Dis. 2012;55(10):1279–1282.