Clinical Decision-Making

Centor and McIsaac: A Testing Decision, Not an Antibiotic Prescription

Use sore-throat scores to guide testing, interpret negative child RADTs and avoid score-only antibiotic decisions.

Quick Medical Calculator Editorial Team · Reading label · 2 min read

Retrospective study sequence, not publication date

Editorial record

This source-linked educational article has been updated through AI-assisted evidence checks and editorial review. Verify information against current guidance and local protocols before applying it to patient care.

Citation methodology

A high sore-throat score is not microbiological confirmation of group A streptococcal (GAS) infection. The practical task is to select appropriate testing and ensure that results lead to follow-up.

What the Score Adds

Centor combines fever above 38 C, tonsillar exudate or swelling, tender anterior cervical nodes, and absence of cough. McIsaac adds age: one point at ages 3-14, no adjustment at 15-44, and subtracts one at 45 or older. Its possible total is -1 to five. A score has different predictive value when local GAS prevalence changes. McIsaac primary validation, IDSA scoring definitions.

The 2025 IDSA update conditionally supports using clinical scores to help determine who should be tested, with very low certainty of evidence. Scores are especially useful for recognizing low-probability presentations, but household GAS exposure, prior rheumatic fever, or possible complicated infection can justify testing even with a low score. This recommendation does not apply to children under three. IDSA risk-assessment recommendation.

Worked Case: The Result Still Matters

A fictional 12-year-old has a temperature of 38.5 C, tonsillar exudate, tender anterior cervical nodes, and no cough. The clinical total is four; age adds one, giving McIsaac 5.

That is a reason to take GAS seriously, not to write "confirmed strep." Under the CDC pathway, arrange appropriate testing. If a rapid antigen detection test (RADT) is negative in a symptomatic child aged three or older, arrange a backup throat culture and a way to contact the family if it becomes positive. A positive RADT or culture supports antibiotic treatment. Routine backup culture after a negative adult RADT is usually unnecessary. Molecular tests have assay-specific pathways; do not assume their negative results follow the RADT rule. CDC clinical guidance.

Avoid Two Common Shortcuts

First, obvious viral features such as cough, rhinorrhea, hoarseness, or oral ulcers may make GAS testing unnecessary. Second, do not use "score four or more" as a universal empirical-antibiotic instruction. The CDC confirmation-based pathway and local policies should be distinguished explicitly, rather than mixed into one table. CDC clinical guidance.

Airway difficulty, inability to swallow secretions, marked unilateral swelling, or systemic deterioration needs urgent assessment for complications, not merely rescoring. Record the testing plan, who will review the result, and what worsening symptoms require reassessment. A low score does not dismiss possible complicated infection. IDSA high-risk exceptions.