Centor score calculator (McIsaac modified)
Estimate the chance of group A streptococcal (GAS) pharyngitis in a child or adult with sore throat. Tick the Centor criteria and pick the age band to see the McIsaac score, the culture-positive rate at that score and the suggested testing from the original CMAJ 1998 study.
Guides
- Centor vs FeverPAIN score for sore throatCentor vs FeverPAIN for sore throat: what each score counts, where FeverPAIN came from, how NICE NG84 uses both, and a patient the two scores disagree on.
How this Centor score calculator works
This Centor score calculator uses the McIsaac version of the score, which adds an age adjustment to the four Centor criteria. Centor and colleagues found in 1981 that four findings predicted a throat culture positive for group A streptococcus in adults with sore throat in an emergency room. McIsaac and colleagues re-derived the same four findings in 1998 from 521 children and adults aged 3 to 76 at a family medicine centre in Toronto, gave each one point, and added points for age because GAS was found in 36.2% of patients aged 3 to 14, 10.7% of those aged 15 to 44 and 1.3% of those aged 45 or older.
McIsaac score = temperature >38 °C + no cough + tender anterior cervical adenopathy + tonsillar swelling or exudate (1 point each) + age points
Age 3–14 years: +1. Age 15–44 years: 0. Age 45 or older: −1. The total runs from −1 to 5; McIsaac counted totals below 0 as 0 and capped the score at 4, so the result bands are 0 or less, 1, 2, 3 and 4 or more.
The original Centor criteria were tonsillar exudates, swollen tender anterior cervical nodes, absence of cough and a history of fever, with no age points. The calculator also shows how many of those four you ticked and the culture-positive rate Centor reported for that count.
Centor and McIsaac score results
The McIsaac score groups patients by the chance that a throat culture grows group A streptococcus. In the 1998 CMAJ study, 65 of 503 patients with complete data (12.9%) were culture positive, ranging from 2.5% at a score of 0 to 52.8% at a score of 4. The study linked each band to a testing step: no culture at 0 or 1, culture everyone at 2 or 3 and treat only if positive, and culture everyone at 4, with treatment allowed on clinical grounds in some patients.
| McIsaac score | Culture positive for GAS | Likelihood ratio | Suggested management in the study |
|---|---|---|---|
| 0 or less | 2.5% (4 of 160) | 0.14 | No culture or antibiotic required |
| 1 | 5.1% (7 of 138) | 0.32 | No culture or antibiotic required |
| 2 | 11.2% (11 of 98) | 0.84 | Culture all; treat only if the culture is positive |
| 3 | 27.8% (15 of 54) | 2.49 | Culture all; treat only if the culture is positive |
| 4 or more | 52.8% (28 of 53) | 6.43 | Culture all; treatment can start on clinical grounds if the patient has a high temperature or is clinically unwell and presents early |
Rates come from Table 2 of McIsaac 1998. Its Figure 1 rounds them to ranges from the two study halves: 2–3% at 0, 4–6% at 1, 10–12% at 2, 27–28% at 3 and 38–63% at 4. Centor's 1981 adult emergency room study reported a positive culture in 2.5% with 0 criteria, 6.5% with 1, 15% with 2, 32% with 3 and 56% with all 4.
When the Centor score is less reliable
The Centor score estimates probability; it does not diagnose strep throat, and even at the top score about half of the McIsaac 1998 patients had a negative culture. The authors warned that the score may overestimate GAS where the infection is less common, and that it should not be used during outbreaks or in populations where rheumatic fever is still a problem. The study included few children and no one under 3, and it excluded patients with bronchitis, otitis media, sinusitis or pneumonia. In a 2004 JAMA validation in 787 patients, McIsaac found that treating adults with a score of 3 or 4 without a test led to many unnecessary antibiotic prescriptions.
The 2012 Infectious Diseases Society of America (IDSA) guideline recommends confirming GAS with a rapid antigen detection test (RADT) and/or culture rather than clinical features alone. It advises a backup culture after a negative RADT in children and adolescents but not routinely in adults, no testing when cough, runny nose, hoarseness or mouth ulcers point to a viral cause, and usually no testing in children under 3.
Questions
What is the difference between the Centor and McIsaac scores?
The Centor score counts four findings, scored 0 to 4, and was derived in adults. The McIsaac score uses the same findings, accepts tonsillar swelling as well as exudate, and adds 1 point for age 3 to 14 and subtracts 1 for age 45 or older, so it can be used in children and adults.
What does a Centor score of 3 mean?
In McIsaac 1998, 27.8% of patients with a score of 3 had a throat culture positive for group A strep. The study suggested a throat culture for everyone at a score of 2 or 3, with treatment only if the culture is positive.
Can the score be below 0 or above 4?
Yes. An adult aged 45 or older with no findings totals −1, and a child aged 3 to 14 with all four findings totals 5. McIsaac counted totals below 0 as 0 and capped the score at 4, so the calculator shows your total and uses the 0 or 4 row for these cases.
Does a high score replace a strep test?
No. At a score of 4, 47.2% of cultures in the 1998 study were negative. The 2012 IDSA guideline recommends a rapid antigen test and/or throat culture to confirm group A strep.
Is my data sent anywhere?
No. The calculation runs in your browser, and the boxes you tick are not sent or stored.
Sources
- Centor RM, Witherspoon JM, Dalton HP, Brody CE, Link K. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981;1(3):239–246. doi:10.1177/0272989X8100100304
- 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 (no DOI; full text PMC1228750)
- 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. doi:10.1001/jama.291.13.1587
- Shulman ST, Bisno AL, Clegg HW, et al. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis. 2012;55(10):e86–e102. doi:10.1093/cid/cis629