What is the purpose and interpretation of the Centor score in diagnosing streptococcal pharyngitis?

Centor Score: Purpose and Clinical Application

What the Centor Score Is

The Centor score is a validated clinical decision tool that stratifies the probability of group A streptococcal (GAS) pharyngitis in adults with sore throat, using four clinical criteria to guide testing and treatment decisions. 1

The four components are:

• Fever by history (1 point)
• Tonsillar exudates (1 point)
• Tender anterior cervical lymphadenopathy (1 point)
• Absence of cough (1 point)

Each criterion receives one point for a maximum score of 4 2, 1.

Risk Stratification and Probability of GAS Infection

The score directly correlates with probability of streptococcal infection:

• Score 0: 1-2.5% risk 2, 1
• Score 1: 5-10% risk 2, 1
• Score 2: 11-17% risk 2, 1
• Score 3: 28-35% risk 2, 1
• Score 4: 51-53% risk 2, 1

These probabilities have been validated in a large-scale study of over 206,000 patients, confirming the score's accuracy across geographically diverse populations 3.

Clinical Decision Algorithm

For scores 0-2 (low probability):

• Do NOT test or treat with antibiotics 1, 4
• Provide symptomatic management with ibuprofen or acetaminophen 4
• The low probability (<17%) does not justify testing or antibiotic exposure 1

For scores 3-4 (higher probability):

• Perform rapid antigen detection test (RADT) 1, 4
• If RADT is positive, treat with penicillin V for 10 days 1, 4
• Throat culture is NOT necessary after a negative RADT in routine practice 1, 4
• The specificity of RADTs is ≥95% with sensitivity of 80-90% 1

Important Clinical Caveats

The Centor score was validated only in adults, not children 2. The modified McIsaac score adds age stratification (adding 1 point for ages 3-14,0 points for ages 15-44, subtracting 1 point for age ≥45) for broader applicability 1.

Even with a score of 4, only about half of patients actually have GAS pharyngitis 2, 3. This means the positive predictive value remains modest, which is why confirmatory testing is recommended rather than empiric treatment 5.

The score has high negative predictive value (81-97%), making it excellent for ruling out streptococcal infection when scores are low 6, 5. This is its primary clinical utility—safely avoiding unnecessary antibiotics and testing 5.

Testing Technique Matters

Both the posterior pharyngeal wall and both tonsils must be swabbed to optimize test accuracy 2, 1. Improper technique reduces sensitivity and can lead to false-negative results 1.

Antibiotic Considerations

When antibiotics are indicated (positive test in patient with score ≥3), remember that benefits are modest:

• Symptom reduction of only 1-2 days 4
• Must weigh against side effects, antibiotic resistance, and costs 1, 4
• Penicillin V remains first-line treatment when antibiotics are warranted 1, 4

Common Pitfalls to Avoid

• Do not treat based on score alone without confirmatory testing when score is 3-4 1
• Do not test patients with scores 0-2—this leads to overtreatment of false positives 1
• Do not assume the score applies to children—different clinical presentations occur in pediatric populations 2
• Do not forget that most sore throats (>65%) are viral and resolve within one week without antibiotics 4