The Centor score (Centor RM et al., Med Decis Making 1981) is a clinical estimate of the probability of streptococcal pharyngitis (GAS, group A β-hemolytic streptococcus) in patients presenting with sore throat. It was modified by McIsaac (CMAJ 1998) with the addition of an age component, hence the name "Centor-McIsaac."
Parameters (1 point each): absence of cough, tonsillar exudate, temperature > 38 °C, tender anterior cervical lymphadenopathy. McIsaac adds: age 3-14 years (+1), 15-44 years (0), ≥ 45 years (-1). Total score ranges from -1 to 5.
Interpretation: ≤ 0 - low probability of GAS, antibiotics not indicated; 1 - low probability, no testing needed; 2-3 - moderate probability, rapid antigen test or culture; ≥ 4 - high probability, empiric antibiotics may be warranted or confirm with rapid testing. Guidelines on acute pharyngitis use the score to support evidence-based antibiotic prescribing.
When to use
Acute sore throat - assessing the need for antibiotic therapy.
Decision to perform a rapid strep test or throat culture for GAS.
Documenting clinical justification for prescribing or withholding antibiotics (antibiotic stewardship).
Screening in outpatient practice and the emergency department.
Parameters in detail
Temperature > 38 °C
Temperature > 38 °C, by history or on examination.
Absence of cough
Absence of cough scores 1 point (presence of cough lowers the likelihood of GAS).
Tonsillar swelling/exudate
Tonsillar exudate or swelling on examination.
Tender anterior cervical lymphadenopathy
Tender, enlarged anterior cervical lymph nodes.
Age group
Age: 3-14 years (+1), 15-44 years (0), ≥ 45 years (-1).
Clinical example
Case
A 9-year-old girl with 2 days of fever up to 38.5 °C, sore throat, no cough. Examination reveals tonsillar exudate and enlarged, tender anterior cervical lymph nodes.
Calculation
Age 3-14 years (1) + temperature (1) + no cough (1) + exudate (1) + lymph nodes (1) = 5 points.
Interpretation and management
High probability of GAS pharyngitis. Management: rapid antigen detection test (if available) or throat culture, with empiric amoxicillin 50 mg/kg/day for 10 days (or phenoxymethylpenicillin) started while awaiting results. For beta-lactam allergy, use a macrolide (azithromycin), accounting for local resistance patterns. Symptomatic treatment (paracetamol/acetaminophen), and monitoring for complications (peritonsillar abscess, poststreptococcal glomerulonephritis, rheumatic fever).
Limitations and cautions
Does not diagnose GAS with certainty; bacteriologic confirmation is required. The score only raises or lowers pretest probability.
Does not distinguish GAS carriage from true infection, risking overtreatment of carriers.
Low specificity in children, in whom viral pharyngitis often mimics streptococcal infection.
According to AAFP/IDSA: ≥ 4 - empiric treatment is reasonable, or perform a rapid test first. 2-3 - treat only after a positive test. 0-1 - do not prescribe, regardless of patient request.
Centor vs McIsaac - which should be used?
McIsaac (with the age adjustment) is more accurate and is the default version used in current guidelines.
Is it applicable in adults older than 45 years?
Yes, but age ≥ 45 years subtracts 1 point, reflecting the lower probability of GAS with increasing age. Most adults with pharyngitis have a viral etiology.
What if the rapid strep test is negative but the Centor score is 4?
Rapid antigen tests have a sensitivity of approximately 85%. With high clinical probability, throat culture (the gold standard) is recommended, and empiric antibiotics may be justified pending the result.
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Aleksandr A. Aulov
Physician, internal medicine, Sechenov School — independent medical education platform.
Calculators are compiled from the original publications and current clinical guidelines. Interpretation thresholds follow the source study unless stated otherwise.
This calculator is intended for healthcare professionals. Do not use it for self-diagnosis or self-treatment. Management decisions are made by the treating clinician based on the full clinical picture of the individual patient.
Last clinical review: April 28, 2026 ·
Author: Aleksandr A. Aulov,
MD, internal medicine ·
Primary source: McIsaac WJ et al. CMAJ 1998; 158(1): 75-83