McIsaac score (modified Centor)
Age-adjusted probability of group A streptococcal pharyngitis from 3 years of age
- DEGAM S3 Halsschmerzen
Sources last checked: 2026-10-13
McIsaac score (modified Centor)
Age-adjusted probability of group A streptococcal pharyngitis from 3 years of age
Original age bands: 3–14 years +1, ≥ 45 years −1. DEGAM paraphrases them as '< 15' and '> 45' years. Not for patients with red flags (scarlet-fever rash, suspected mononucleosis, immunosuppression, severe comorbidity). The DEGAM S3 guideline is past its review date and under revision.
Interpretation
| ≤ 2 — low probability | Group A streptococci in ≈ 8 % (≤ 0), 14 % (1) and 23 % (2) of patients ≥ 3 years (Fine 2012; pooled 11 % in DEGAM). DEGAM recommends symptomatic treatment only in this group. |
|---|---|
| 3 — intermediate probability | Group A streptococci in ≈ 37 %. DEGAM provides for an antibiotic only as a delayed prescription and notes that in children and adolescents aged 3–15 a rapid antigen test may support the decision. |
| 4–5 — higher probability | Group A streptococci in ≈ 55 %. DEGAM names a delayed or immediate antibiotic as options and notes that in children aged 3–15 a rapid antigen test may support the decision. |
What is the McIsaac score (modified Centor)?
The McIsaac score is an age-adjusted version of the Centor score. McIsaac and colleagues developed it in 1998 in a Toronto family-medicine centre in patients aged 3 to 76 years, adding a point for children and subtracting one for older adults. Fine and colleagues validated it in 2012 in more than 200,000 patients.
When to use it
- Acute sore throat in children from 3 years and in adults.
- Primary care decisions on symptomatic treatment, delayed prescription or immediate antibiotic.
- Selecting children in whom a rapid streptococcal antigen test is worthwhile.
When not to use it
- Children under 3 years — group A streptococcal pharyngitis is rare and the score was not designed for them.
- Red flags such as scarlet-fever rash, suspected mononucleosis or immunosuppression.
- Recurrent tonsillitis or suspected complications.
How it is calculated
| Criterion | Points |
|---|---|
| Temperature > 38 °C | +1 |
| Absence of cough | +1 |
| Swollen, tender anterior cervical lymph nodes | +1 |
| Tonsillar swelling or exudate | +1 |
| Age | |
| 3–14 years | 1 |
| 15–44 years | 0 |
| ≥ 45 years | -1 |
Clinical pearls and limitations
- Original age bands: 3–14 years +1, ≥ 45 years −1. DEGAM paraphrases them as '< 15' and '> 45' years. Not for patients with red flags (scarlet-fever rash, suspected mononucleosis, immunosuppression, severe comorbidity). The DEGAM S3 guideline is past its review date and under revision.
- Possible range is −1 to 5; scores of 4 and 5 are grouped together.
- Age bands in the original: 3–14 years (+1), 15–44 years (0), ≥ 45 years (−1).
- DEGAM treats McIsaac, Centor and FeverPAIN as interchangeable for the treatment decision.
- Group A streptococcal prevalence in children is higher (20–40 %) than in adults — hence the extra point.
Frequently asked questions
Is McIsaac the same as the modified Centor score?
Yes. 'Modified Centor' and 'McIsaac score' describe the same five-item score with the age adjustment.
How likely is strep throat with a McIsaac score of 3?
About 37 % in the large 2012 validation; at 4 or more it was about 55 %.
Can the score be negative?
Yes, a patient aged 45 or older with no clinical criterion scores −1, the lowest-risk category.
Evidence and guidelines
- Primary source: 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.
- Fine AM, Nizet V, Mandl KD. Large-scale validation of the Centor and McIsaac scores to predict group A streptococcal pharyngitis. Arch Intern Med 2012;172(11):847-852.
- McIsaac WJ, Kellner JD, Aufricht P, Vanjaka A, Low DE. Empirical validation of guidelines for the management of pharyngitis in children and adults. JAMA 2004;291(13):1587-1595.
- DEGAM S3-Leitlinie Halsschmerzen (AWMF-Register 053-010), 2020, revidiert 12/2021 — Empfehlung 9.9 und Tabelle 8.2. Gültigkeit abgelaufen, in Überarbeitung.
Have a follow-up question?
Medelix answers clinical questions from current guidelines and studies — every statement with its source.
Related calculators
Embed this calculatorFree to use on your website, intranet or teaching page. Copy the code below.
<iframe src="https://medelix.ai/en/embed/mcisaac" title="McIsaac score (modified Centor) – Medelix" width="100%" height="620" style="border:0;max-width:720px" loading="lazy"></iframe>
<p><a href="https://medelix.ai/en/calculators/mcisaac-score">McIsaac score (modified Centor) calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.