Centor Score (Modified/McIsaac)
Likelihood of streptococcal pharyngitis and need for testing/antibiotics
Calculator
Why use it
Reduces unnecessary antibiotic prescriptions for viral pharyngitis. Guides appropriate use of rapid strep testing. Cost-effective approach to sore throat management.
About
The Modified Centor Score (McIsaac) estimates the probability of group A streptococcal (GAS) pharyngitis in patients with sore throat. It guides decisions about rapid antigen testing and empiric antibiotic use. The modification adds an age criterion to the original four Centor criteria.
When to use
- Acute sore throat / pharyngitis evaluation
- Deciding whether to perform rapid strep test or throat culture
- Antibiotic decision-making for pharyngitis
Formula
Pearls & pitfalls
- Score 0-1 has < 10% probability of GAS — testing and antibiotics are NOT recommended.
- Most sore throats are viral — antibiotics provide no benefit and contribute to resistance.
- The original Centor criteria did not include age; McIsaac modification adds +1 for age 3-14 and -1 for ≥ 45.
- IDSA guidelines recommend testing (RADT ± culture) rather than empiric treatment, even with high scores.
- Consider Fusobacterium necrophorum (Lemierre syndrome) in adolescents with severe pharyngitis.
- Rapid strep test sensitivity is ~85-90%; consider throat culture backup in children with negative RADT.
Next steps
Score 0-1: No testing or antibiotics needed (risk < 10%). Score 2-3: Rapid antigen test; treat if positive. Score 4-5: Consider empiric antibiotics or test-and-treat.
Evidence
Original Centor criteria (1981) validated for adult pharyngitis. McIsaac modification (1998) added age criterion, validated in 521 patients. IDSA 2012 guidelines incorporate the score for pharyngitis management.