Centor / McIsaac (strep pharyngitis)
Centor strep-pharyngitis score (tonsillar exudate, tender anterior adenopathy, fever history, absence of cough; 1 each) with the McIsaac age modifier (3-14 years +1, >= 45 years -1) computed from the same criteria.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Tonsillar exudate
- Yes
- Tender anterior cervical adenopathy
- Yes
- History of fever > 38 C
- Yes
- Absence of cough
- Yes
- Age
- 12 years
Result: Centor 4; McIsaac 5 (high probability of GAS pharyngitis; consider testing or empiric treatment).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- <=1 (McIsaac)
- Low probability of GAS pharyngitis. No further testing or antibiotics per source.
- 2-3 (McIsaac)
- Intermediate probability. Rapid antigen detection test or throat culture per source.
- 4-5 (McIsaac)
- High probability of GAS pharyngitis. Empiric treatment may be considered per source; testing remains an option.
What you enter
- Tonsillar exudate (1)
- Tender anterior cervical adenopathy (1)
- History of fever > 38 C (1)
- Absence of cough (1)
- Age (McIsaac modifier)
What this is
Score the four-criterion Centor rule for adult pharyngitis with the McIsaac age adjustment: one point each for tonsillar exudate, tender anterior cervical lymphadenopathy, history of fever, and absence of cough; plus one point for age 3-14, zero points for 15-44, and minus one point for >=45. Sophie Well returns the total score, the IDSA / CDC-aligned probability band for group A streptococcus, and the testing and treatment recommendation that pairs with that band.
When to use it
Use this for a primary-care or urgent-care visit for sore throat to decide whether the encounter needs a rapid strep test, a culture, empiric antibiotics, or symptomatic care only. The score is calibrated for ambulatory adults and older children with acute pharyngitis - it is not validated for immunocompromised hosts, recurrent tonsillitis under chronic management, or patients with peritonsillar abscess or other suppurative complications. A score in the low band predicts strep prevalence under 10% and is the strongest tool clinicians have for not prescribing antibiotics in viral pharyngitis.
How this is calculated
Centor RM, et al. Med Decis Making. 1981;1(3):239-246. McIsaac WJ, et al. CMAJ. 1998;158(1):75-83. Read the sources: Centor 1981 ↗, McIsaac 1998 ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.