How is the Centor score interpreted?

Score 0–1: GAS unlikely (~5–10%), no testing or antibiotics needed. Score 2–3: Moderate probability (~15–35%), rapid antigen testing recommended. Score 4–5: High probability (~50%), empiric antibiotics or test-and-treat approach. Guidelines recommend throat culture confirmation for negative rapid tests in children.

Should you always test for strep with a high Centor score?

Guidelines vary. The IDSA recommends testing (rapid antigen ± culture) regardless of score and treating only confirmed cases. The ACP/ESCMID supports empiric treatment for scores ≥ 4 in some settings. Testing helps avoid unnecessary antibiotics and confirms diagnosis.

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Modified Centor Score (McIsaac)

Estimate the probability of Group A Streptococcal (GAS) pharyngitis and guide testing/treatment decisions.

Criteria

Age

Tonsillar exudates or swelling (+1) Tender anterior cervical lymphadenopathy (+1) Fever (temperature > 38°C / 100.4°F) (+1) Absence of cough (+1)

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Select age group to begin scoring.

≤ 0~1–2.5% GAS risk — no testing or antibiotics

1~5–10% — no testing or antibiotics

2~11–17% — optional rapid strep test

3~28–35% — rapid strep test recommended

≥ 4~51–53% — rapid strep test or empiric Rx

Disclaimer: For educational purposes only. Not a substitute for clinical judgment.

When to use

Use in patients presenting with sore throat to determine whether to test for GAS and/or initiate empiric antibiotics. Particularly useful in primary care and urgent care settings.

Clinical pearls

IDSA guidelines recommend AGAINST empiric antibiotics without testing (rapid strep or throat culture) in adults.
Score ≤ 1: GAS unlikely — neither testing nor antibiotics recommended.
Score 2–3: Test with rapid antigen detection; treat if positive.
Score ≥ 4: Empiric treatment reasonable while awaiting test results in some guidelines.
The McIsaac modification adds age as a criterion to improve specificity in adults (who have lower GAS prevalence).

References

Centor RM, et al. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981;1(3):239-246.
McIsaac WJ, et al. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998;158(1):75-83.

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About This Tool

What Is the Centor Score?

The Centor Score is a clinical prediction rule originally developed by Centor et al. in 1981 to estimate the probability of Group A Streptococcal (GAS) pharyngitis in patients presenting with sore throat. The original score used four criteria: tonsillar exudates, tender anterior cervical lymphadenopathy, fever, and absence of cough. In 1998, McIsaac modified the score by adding age as a fifth criterion, improving its accuracy across age groups. The Modified Centor (McIsaac) Score is now the standard version used in clinical practice.

Scoring and Interpretation

The score ranges from −1 to 5. Age contributes +1 point for ages 3–14, 0 for ages 15–44, and −1 for age ≥ 45. Each clinical criterion (exudates, lymphadenopathy, fever, absence of cough) adds 1 point when present. The estimated probability of GAS pharyngitis increases with the score: ≤ 0 (~1–2.5%), 1 (~5–10%), 2 (~11–17%), 3 (~28–35%), and ≥ 4 (~51–53%). Management recommendations vary: scores ≤ 1 suggest no testing needed, scores 2–3 warrant rapid strep testing, and scores ≥ 4 may justify empiric treatment in some guidelines.

Guideline Recommendations

The Infectious Diseases Society of America (IDSA) and the American Heart Association recommend against empiric antibiotic treatment for adults without confirmatory testing (rapid antigen or throat culture), regardless of Centor score. However, some international guidelines and the ACP/CDC "Choosing Wisely" approach allow for empiric treatment at high scores. In children (3–14 years), GAS prevalence is higher, and throat culture backup of negative rapid tests is recommended given the higher risk of rheumatic fever. The primary goal of GAS treatment is preventing rheumatic fever, suppurative complications, and reducing symptom duration.

🔑 Clinical Pearls

Score ≤ 1 reliably excludes GAS in adults — avoid unnecessary antibiotics and testing.
IDSA guidelines recommend confirmatory testing even at high scores in adults before prescribing antibiotics.
In children, negative rapid strep should be backed up by throat culture — rapid tests have ~15% false-negative rate.
The absence of cough is a positive criterion — cough suggests viral etiology, making GAS less likely.

Key References

Centor RM, et al. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981;1(3):239-246.
McIsaac WJ, et al. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998;158(1):75-83.
Shulman ST, et al. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by IDSA. Clin Infect Dis. 2012;55(10):e86-e102.

Formula last verified: February 2026