About the Centor Score Calculator
The Centor score estimates how likely a sore throat is to be caused by group A streptococcus ("strep throat") rather than a virus. The original Centor criteria (1981) give one point each for fever, absence of cough, tender swollen front-of-neck lymph nodes, and tonsillar swelling or exudate. McIsaac and colleagues later added an age adjustment — plus one point for ages 3–14 and minus one for 45 and over — creating the modified Centor or McIsaac score, which works for children as well as adults.
This calculator gives both scores and the proportion of patients at each McIsaac score whose throat culture grew group A strep in McIsaac’s 2000 validation study of 621 children and adults seen in Ontario family practices. It is intended for clinicians, students and curious patients deciding whether a sore throat warrants a rapid strep test or culture.
The score estimates probability only — confirmation requires a rapid antigen test or throat culture, and decisions about testing and treatment belong to a clinician following local guidelines. The score was not designed for children under 3, for people with immune suppression, or during outbreaks of rheumatic fever.
With the default inputs, the mcisaac (modified centor) score is 3. Change any value above to recalculate instantly.
How to use the centor score calculator
- 1Enter the patient’s age.
- 2Record whether the temperature has been 38 °C (100.4 °F) or higher.
- 3Note whether cough is absent.
- 4Examine the front of the neck for tender, swollen lymph nodes and the tonsils for swelling or exudate.
- 5Read the McIsaac score and the culture-positive rate at that score.
Formula and method
Each clinical criterion present scores one point: temperature of 38 °C or higher (history or measured), absence of cough, tender anterior cervical lymphadenopathy, and tonsillar swelling or exudate. The original Centor score stops there and was derived in adults attending an emergency department. McIsaac’s modification adds one point for patients younger than 15 and subtracts one for patients 45 or older, reflecting how strep prevalence falls with age.
In McIsaac’s 2000 family-practice validation, group A streptococcus was cultured in 1% of patients scoring 0 or less, 10% at 1, 17% at 2, 35% at 3 and 51% at 4 or more. These percentages depend on local prevalence and season, so treat them as approximate.
- fever
- 1 if temperature ≥ 38 °C
- no cough
- 1 if cough is absent
- nodes
- 1 if tender, swollen anterior cervical lymph nodes
- tonsils
- 1 if tonsillar swelling or exudate
Worked examples
25-year-old with fever, no cough and exudate
Fever, absent cough and tonsillar exudate score three points; nodes are not tender. Age 25 adds nothing, so both scores are 3. In the validation study, 35% of patients with a score of 3 had group A strep on culture.
8-year-old with all four criteria
All four Centor criteria are present (score 4), and being under 15 adds one point for a McIsaac score of 5. About half (51%) of patients scoring 4 or more had a positive culture.
52-year-old with cough and sore throat
Only tonsillar swelling is present (Centor 1), and age 45 or over subtracts one point, giving a McIsaac score of 0. Just 1% of patients at 0 or below had strep on culture.
Frequently asked questions
What is the difference between the Centor and McIsaac scores?+
The Centor score uses four clinical findings and was developed in adults. The McIsaac (modified Centor) score adds an age adjustment — +1 under 15, −1 at 45 or older — so it can be used in children aged 3 and over.
What Centor score means strep throat?+
No score confirms strep. Even at 4 or more, only about half of patients had a positive culture in McIsaac’s study. A rapid antigen detection test or throat culture is needed for diagnosis.
What does a Centor score of 0 or 1 mean?+
Strep is unlikely: about 1% at 0 and 10% at 1 in the validation study. Most sore throats at these scores are viral and settle on their own within a week.
Does the Centor score work for young children?+
The McIsaac version was validated from age 3. Strep throat is uncommon in children under 3, and guidelines generally do not recommend routine testing in that age group.
What is the FeverPAIN score?+
FeverPAIN is a UK alternative that scores fever, purulence, rapid attendance, inflamed tonsils and no cough or coryza. NICE accepts either FeverPAIN or Centor for assessing sore throat.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.