Centor Score & Modified McIsaac Score for Strep Pharyngitis
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About the Centor & McIsaac Scores
The Centor score and its modified version (McIsaac score) are clinical prediction rules used to estimate the probability of group A β-hemolytic streptococcal (GABHS) pharyngitis in patients presenting with sore throat. These tools help clinicians make evidence-based decisions about when to test for and treat strep throat.
Clinical Significance
Group A streptococcal pharyngitis accounts for approximately 5-15% of sore throats in s and 20-30% in children. Accurate diagnosis is important to prevent overuse of antibiotics and to identify patients who may benefit from treatment to prevent complications like rheumatic fever.
Centor Criteria
The original Centor score includes 4 criteria:
- Fever (temperature > 38°C/100.4°F)
- Absence of cough
- Tender anterior cervical adenopathy
- Tonsillar exudate or swelling
McIsaac Modification
The McIsaac score adds one additional criterion to the Centor score:
- Age 3-14 years: +1 point
- Age 15-44 years: 0 points
- Age 45+ years: -1 point
Interpretation & Management
| Score | Risk of Strep | Recommended Management |
|---|---|---|
| 0-1 | 1-10% | No testing or antibiotics needed |
| 2 | 11-17% | Consider rapid strep testing |
| 3 | 28-35% | Perform rapid strep testing or throat culture |
| 4-5 (McIsaac) | 51-53% | Consider empiric treatment or testing |
Evidence & Validation
These scoring systems have been validated in multiple clinical settings. The original Centor criteria were published in 1981 and were later modified by McIsaac in 1998 to account for age-related differences in strep throat prevalence.
Limitations
- Cannot definitively rule in or rule out strep throat
- Less reliable in areas with high rheumatic fever prevalence
- Does not account for carrier states
- Clinical findings can be subjective
- Not validated for determining need for antibiotics in all populations
Clinical Tips
- Remember that most sore throats are viral and do not require antibiotics
- Consider local antibiotic resistance patterns when making treatment decisions
- Patients with history of rheumatic fever may need a lower threshold for testing and treatment
- Pharyngitis with high-risk features (e.g., toxic appearance, difficulty handling secretions) requires immediate evaluation regardless of score