Centor Score Calculator (Modified/McIsaac)

Enter age and four clinical signs to calculate the Centor/McIsaac score for sore throat and see the estimated risk of group A streptococcal (strep) pharyngitis.

Quick Facts

Original Centor criteria (1 pt each)
Exudate, tender nodes, fever, absent cough
Four signs identified by Centor in 1981 to estimate probability of strep pharyngitis in adults.
McIsaac age adjustment
+1 (age 3-14), 0 (15-44), -1 (≥45)
Added in 1998 to extend the score to children as young as 3 and to older adults.
Score range
-1 to +5 points
Higher totals correlate with a higher likelihood of group A strep.

Your Results

Calculated
Centor/McIsaac Score
-
Sum of criteria points plus age adjustment
Estimated Strep Risk
-
Approximate probability of group A strep
Risk Category
-
Based on published McIsaac score bands
Suggested Next Step
-
Educational guidance, not a prescription

Ready

Enter age and the four clinical signs, then press Calculate. This tool is educational and does not replace testing or a clinician's evaluation.

How the Centor/McIsaac Score Works

The Centor score was developed by Robert Centor in 1981 to estimate, from four bedside signs, how likely an adult's sore throat is caused by group A streptococcus rather than a virus. In 1998, Warren McIsaac added an age adjustment, extending the tool's use to children age 3 and up and refining it for older adults. Each of the four clinical criteria is worth one point, and the age adjustment adds or subtracts a point, producing a total score from -1 to +5 that maps to a published estimated probability of strep pharyngitis.

The four criteria and the age adjustment

  • Tonsillar exudate or swelling — visible white patches, pus, or marked swelling on the tonsils: +1 point.
  • Tender or swollen anterior cervical lymph nodes — tenderness along the front of the neck: +1 point.
  • Fever — a measured temperature above 38°C (100.4°F), or a reported history of fever: +1 point.
  • Absence of cough — strep pharyngitis rarely causes a cough, so no cough at all: +1 point.
  • Age adjustment (McIsaac) — age 3-14: +1 point; age 15-44: 0 points; age 45 and older: -1 point.

Interpreting your score

Add the criteria points to the age adjustment to get a total from -1 to +5. Published McIsaac cohort data associate each total with an approximate probability of group A strep: 0 or below is roughly 1-2.5% risk, 1 point is about 5-10%, 2 points is about 11-17%, 3 points is about 28-35%, and 4 or 5 points is about 51-53%. Many clinical pathways use this to decide next steps — low scores generally support skipping testing and antibiotics, middle scores support a rapid antigen test or throat culture before treating, and high scores support testing or, in some protocols, empiric antibiotic therapy pending test results.

When to consult a professional

This calculator is an educational tool that reproduces a published clinical scoring system — it is not a diagnosis and does not replace a rapid strep test, throat culture, or a clinician's exam. Sore throats can also result from other causes that a score alone cannot rule out. If symptoms are severe (difficulty breathing or swallowing, drooling, or a muffled voice) seek urgent medical care; otherwise, discuss testing and treatment options with a licensed healthcare provider.

Frequently Asked Questions

What is the Centor score used for?
The Centor score estimates the probability that a sore throat is caused by group A streptococcus (strep throat) rather than a virus, based on four clinical signs: tonsillar exudate, tender anterior cervical lymph nodes, fever, and absence of cough. Clinicians use it to decide whether testing or antibiotics are warranted.
What is the difference between the Centor score and the McIsaac score?
The original 1981 Centor score used four criteria and was validated only in adults. In 1998, McIsaac added an age adjustment (+1 for ages 3-14, 0 for ages 15-44, -1 for age 45 and older), which extends the tool to children as young as 3 and improves accuracy across all ages.
What does my Centor/McIsaac score mean?
Higher scores correlate with a higher chance of group A strep: a score of 0 or less suggests roughly 1-2.5% risk, 1 point suggests about 5-10%, 2 points about 11-17%, 3 points about 28-35%, and 4 or 5 points about 51-53%. Lower scores generally support skipping testing and antibiotics; higher scores support testing or, in some protocols, empiric treatment.
Can this calculator diagnose strep throat?
No. The Centor/McIsaac score is a clinical decision-support estimate, not a diagnosis. A rapid antigen detection test or throat culture is needed to confirm group A strep, and any testing or treatment decision should be made with a licensed clinician.

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