Primary Care
Centor Score (McIsaac modified)
Likelihood of streptococcal pharyngitis.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The Centor score, with the McIsaac modification, estimates the likelihood that a sore throat is caused by group A streptococcal infection, helping to target testing and antibiotic prescribing. The original Centor criteria award one point each for tonsillar exudate, tender anterior cervical lymphadenopathy, fever over 38°C and absence of cough. McIsaac added an age adjustment: a point for ages 3–14 and a point subtracted for ages 45 and over. The total ranges from −1 to 5.
Interpreting the result
A low score (−1 to 1) carries a low probability of streptococcal infection, and testing or antibiotics are usually not needed. An intermediate score (2–3) raises the probability and supports considering a rapid antigen test or throat swab. A higher score (4–5) indicates the greatest likelihood and may justify testing or empirical treatment within local pathways. The score raises or lowers pre-test probability but never confirms infection on its own.
Advice
Follow local antimicrobial guidance (e.g. NICE FeverPAIN/Centor pathways). A high score raises pre-test probability but does not confirm streptococcal infection.
Worked example
A 10-year-old with tonsillar exudate (1), tender cervical nodes (1), fever above 38°C (1), no cough (1) and age 3–14 (1) scores 5. This is the highest band, supporting a rapid test or, per local guidance, empirical antibiotic treatment.
Pearls / pitfalls
- A high score increases probability but does not confirm streptococcal infection; many high-scoring sore throats remain viral.
- The age adjustment matters — omitting it overestimates risk in adults over 45 and underestimates it in young children.
- NICE pathways often favour FeverPAIN; check which tool your local guidance specifies.
- It does not assess for complications such as peritonsillar abscess or airway compromise, which require separate clinical evaluation.
Evidence & validation
The original criteria were described by Centor and the age modification validated by McIsaac and colleagues, reducing unnecessary antibiotic use. In UK practice it is used alongside the FeverPAIN score within NICE guidance on sore throat and antimicrobial stewardship.
Frequently asked questions
What is the difference between Centor and McIsaac?
McIsaac is a modification of the original Centor criteria that adds an age adjustment — a point for ages 3–14 and a point subtracted for ages 45 and over. This improves accuracy across the age range.
Does a high score mean I need antibiotics?
Not necessarily. A high score raises the likelihood of streptococcal infection and may support testing or treatment, but the decision follows local antimicrobial guidance and considers the overall clinical picture.
How does it compare with FeverPAIN?
Both estimate the likelihood of streptococcal sore throat to guide antibiotic decisions. NICE guidance commonly uses FeverPAIN, but either tool aims to reduce unnecessary prescribing; follow local policy.
Can it be used in young children?
The McIsaac modification extends use to children from age 3, giving a point for ages 3–14. Sore throat in very young children and any signs of serious illness still need careful clinical assessment.
Does the score diagnose tonsillitis?
No. It only estimates the probability of group A streptococcal infection. A confirmed diagnosis requires a rapid antigen test or throat swab where indicated.
References
- McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998;158(1):75–83.
- NICE NG84: Sore throat (acute): antimicrobial prescribing. 2018.
About the creator
McIsaac WJ et al.
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