For healthcare professionals
Centor score calculator (McIsaac score)
The Centor score and its age-adjusted version, the McIsaac score, estimate how likely a sore throat is to be caused by group A streptococcus (strep throat) from four signs and symptoms. They help clinicians decide who needs a throat swab test. This calculator is written for clinicians and is not a diagnosis; only a rapid antigen test or throat culture confirms strep.
Signs and symptoms
For patients aged 3 and older with a new sore throat. Nothing you enter leaves this page.
What you will see
The McIsaac score (and the Centor score from age 15), the share of patients with group A strep at that score in published validations, and the management the McIsaac authors suggested.
Educational only, not medical advice. Not a diagnosis. A rapid antigen test or throat culture confirms strep.
Source
McIsaac WJ et al., CMAJ 2000, Methods, for the five McIsaac items, the age adjustment and the suggested management; Fine AM et al., Arch Intern Med 2012 for the four Centor items and the group A strep percentages by score. The tests check each item, the age cut points and the score bands.
Validated in
McIsaac score: derived in 521 patients aged 3 to 76 at a university family medicine centre in Toronto (1995 to 1997) and validated in 621 children and adults seen by 97 family physicians in 49 Ontario communities. Both scores: validated in 206,870 patients aged 3 and older tested for strep at a US retail health chain (2006 to 2008); the Centor score in those aged 15 and older.
Limits
Estimates the chance of group A strep only; it does not diagnose strep or rule out other causes of sore throat. Studied in patients aged 3 and older presenting to primary care or retail clinics; percentages depend on local strep prevalence and season. Patients who looked septic were referred out of the retail clinic study. General safety advice (not part of the published score): trouble breathing, drooling, being unable to swallow or open the mouth fully, or a stiff neck need urgent care, not a score.
Centor and McIsaac criteria
Score 1 point for each item present. The Centor score uses the first four items (0 to 4) (Fine 2012). The McIsaac score counts tonsillar swelling or exudate and adds an age adjustment, for a total from -1 to 5 (McIsaac 2000).
| Item | Centor | McIsaac |
|---|---|---|
| Fever (history of, or measured 38 °C or higher) | 1 | 1 |
| Absence of cough | 1 | 1 |
| Swollen, tender anterior cervical lymph nodes | 1 | 1 |
| Tonsillar exudate | 1 | 1 |
| Tonsillar swelling without exudate | 0 | 1 |
| Age 3 to 14 years | not used | +1 |
| Age 15 to 44 years | not used | 0 |
| Age 45 years or older | not used | -1 |
Sources: score items and age adjustment from the McIsaac validation paper (McIsaac 2000); Centor items as defined in the 2012 large-scale validation (Fine 2012). The McIsaac score was first derived in 521 Toronto family practice patients aged 3 to 76 (McIsaac 1998).
Chance of group A strep by score
| Score | McIsaac, Ontario 2000 | McIsaac, US 2012 | Centor (age 15+), US 2012 |
|---|---|---|---|
| 0 or less | 1% | 8% | 7% |
| 1 | 10% | 14% | 12% |
| 2 | 17% | 23% | 21% |
| 3 | 35% | 37% | 38% |
| 4 or more | 51% | 55% | 57% |
Ontario column: share of cultured throat swabs positive for group A strep in 600 family practice patients (McIsaac 2000). US columns: share testing positive (rapid antigen test, with a DNA probe or culture to confirm negatives) among patients at a national retail health chain; McIsaac scores of -1 and 5 were grouped with 0 and 4 (Fine 2012).
How the McIsaac authors suggested using it
In the 2000 validation, the authors suggested: a score of 1 or less, no throat culture and no antibiotic; 2 or 3, a throat culture with the antibiotic decision based on the result; 4 or more, either starting an antibiotic or taking a culture (McIsaac 2000). Used this way in Ontario practices, the score would have cut antibiotic prescriptions by about half compared with usual care, with a sensitivity of 85.0% and specificity of 92.1% for the score approach (McIsaac 2000). Testing and treatment thresholds differ between national guidelines; follow your local guideline.
In the 2012 validation, the area under the curve was 0.72 for the Centor score (age 15 and older) and 0.71 for the McIsaac score (age 3 and older). The authors noted that the data could not detect other bacterial causes such as group C streptococcus or Fusobacterium necrophorum, and did not address people who carry strep without being ill (Fine 2012).
Related tools
For other infection scores on this site, see the qSOFA score calculator for adults with suspected infection and the CURB-65 calculator for pneumonia severity. For more clinician scores, see the HEART score calculator, the Wells score for PE the creatinine clearance calculator and the Alvarado score calculator for suspected appendicitis.
Sources
- McIsaac WJ, Goel V, To T, Low DE. The validity of a sore throat score in family practice. CMAJ. 2000;163(7):811-815. PMID 11033707. Methods (score items and suggested management) and Results (group A streptococcus by score). pmc.ncbi.nlm.nih.gov/articles/PMC80502/
- 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. PMID 9475915. Abstract (derivation: 521 patients aged 3 to 76, Toronto). pmc.ncbi.nlm.nih.gov/articles/PMC1228750/
- 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. doi:10.1001/archinternmed.2012.950. PMID 22566485. NIH author manuscript: abstract, introduction and methods (score definitions), results. pmc.ncbi.nlm.nih.gov/articles/PMC3627733/
Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-01. Spotted an error? See About.