The Centor and McIsaac Score: The Evidence Behind the Tool

A 12-year-old boy is brought to the taluk hospital OPD by his mother. He has had a sore throat for two days. His temperature is 38.6 C. His tonsils are swollen with white exudate, the nodes at the front of his neck are tender, and he has no cough. His mother wants an injection, “so that it goes quickly”. The intern beside you asks, “Sir, is this strep throat? Do we give antibiotics?” This is an illustrative case, not a real patient.

Most sore throats are viral, and antibiotics do nothing for them. A few are caused by group A streptococcus, and in a child in India those few matter, because untreated they can lead to rheumatic fever and rheumatic heart disease. The Centor and McIsaac score helps you decide which sore throats are worth testing. By the end of this article you will know what the score can tell you, how well it worked in Indian children, and what to do when the test it points to is not available.

1. How the score was built

Centor and his colleagues derived four findings in adults who came to an emergency room with a sore throat (Centor 1981): tonsillar exudate or swelling, tender and swollen anterior cervical nodes, a documented fever above 100.4 F (38.0 C), and the absence of cough. Each scores one point. McIsaac added an age adjustment in 1998, so that the same findings would work in children, in whom group A streptococcus is more common, and in older adults, in whom it is less so. Ages 3 to 14 add a point, ages 15 to 44 add nothing, and 45 and above take a point away.

Notice what both papers were trying to do. The goal was fewer unnecessary antibiotics for a sore throat that is very unlikely to be streptococcal. The score was not built to find every case, and it was not built to weigh the risk of rheumatic fever.

Our boy has all four findings, and his age adds one. His total is 5. The tool puts every total of 4 or more in the top band.

This is the table the tool uses, the McIsaac bands.

“Wait, even with a score of 5 it is only about half?” Yes. That surprises most people. Even with every finding present, about half of these throats are not streptococcal. That is why the tool reads the higher bands as “worth testing” rather than “treat now”: a rapid antigen test or a culture is more accurate than the score at any point value. The score’s real strength is at the bottom. A score of 0 or 1 makes streptococcus unlikely enough that neither a test nor an antibiotic is needed.

2. Does it work in Indian children?

Every one of those bands comes from Canadian family practice. Does it travel? There is one Indian study to go on. A 2019 study of 120 children in Chennai found the modified Centor score performed poorly as a standalone predictor of culture-confirmed streptococcal pharyngitis in that population.

What do those numbers mean? Area under the curve 0.589, with a confidence interval crossing 0.5. Culture positivity in the cohort was 35 per cent.

The area under the curve is a single number for how well a test separates people with a disease from people without it. A perfect test scores 1. A coin toss scores 0.5. A score of 0.589, with a confidence interval that crosses 0.5, means that in this group of children the score could not be shown to do better than chance. Notice also that about one child in three in that cohort had a positive culture.

The same study found that resistance was highest for cotrimoxazole, at 16.7 per cent, and that resistance to fluoroquinolones and macrolides was high among the streptococci isolated. Hold on to that. It matters when we choose a drug.

“So should we stop using the score?” Not quite. This is one cohort of 120 children in one city, not a national figure. What it tells us is to treat the score as one input to the decision to test, not as a substitute for testing. The largest validation adds a caution of its own. In a United States study of 206,870 patients (Fine 2012), the figure at a score of 0 was 8 per cent, against 1 to 2.5 per cent in the McIsaac bands. The tool keeps that comparison in its Evidence tab, because it falls in the band where the tool advises against testing.

3. When there is no test

Here is the difficulty. The bands send you to a rapid antigen test or a throat culture. In the ICMR Standard Treatment Workflow, a throat swab for culture is essential and the rapid antigen test is optional. In practice, a rapid antigen test is not stocked in most district and taluk hospitals. A culture takes 24 to 48 hours.

Two respected bodies part company on what to do then. IDSA 2012 would not treat without a positive test. WHO 2024 recommends that, in populations at moderate to high risk of rheumatic fever and where testing is not available, children and adolescents with clinically suspected streptococcal pharyngitis should be treated with antibiotics. The tool prints the IDSA position on the result and sets out the WHO position beside it, so that neither is applied without the reader knowing the other exists. Which one this boy’s doctor follows is a judgement about where he lives.

“If we send a culture, are we not delaying treatment?” Less than you might think. Starting penicillin within nine days of the onset of illness still prevents rheumatic fever (IDSA 2012). There is time to wait for a culture, if the family can come back for the result.

4. If you treat, treat for ten days

This is the most common mistake on our wards and in our OPDs, and it is a kind one: the child looks better in three days, so five days of amoxicillin feels like plenty. It settles the symptoms. It is not equivalent for preventing rheumatic fever. Ten days is the duration that prevents rheumatic fever. Azithromycin is the one exception, its five-day course being the licensed regimen.

The mother who asked for an injection was not wrong. A single intramuscular dose of benzathine penicillin G removes the problem of a child who stops the tablets on day four. Under 27 kg the dose is 6 lakh units; at 27 kg and above it is 12 lakh units. Before the injection, the tool sets out the IAP 2008 test dose with benzylpenicillin, and wherever the injection is given, adrenaline and a resuscitation trolley belong in the room.

And the resistance from Chennai? It is why the tool calls azithromycin the least secure of its options, a fallback for an immediate-type penicillin allergy and not a convenient alternative to a 10-day course.

Back to the boy

His score is 5, in the top band, about half. The tool advises a test and treatment on a positive result. It also prints where the guidance differs at the top: the ICMR Standard Treatment Workflow of 2019 allows antibiotics before the result at a Centor score of 4, which he has, and IDSA 2012 recommends against, treating only proven episodes. If a culture can be sent and the family can return, send it; there is time. If no test can be had, he is in exactly the group where WHO 2024 recommends treating on clinical suspicion: a child, in a population at real risk of rheumatic heart disease, with no test. If he is treated, it is penicillin for ten days, or a single dose of benzathine penicillin, 12 lakh units if he weighs 27 kg or more.

Try this

A 50-year-old woman has a sore throat, a temperature of 38.4 C and a cough. There is no exudate and her nodes are not tender. What is her score, and what does the tool advise? Illustrative case.

Answer. Fever scores 1. Exudate, tender nodes and absence of cough score nothing, because she has a cough. Her age, 45 or above, takes a point away. Her total is 0: an estimated 1 to 2.5 per cent, no testing and no antibiotics.

Take-home points

• The score is strongest at the bottom: a total of 0 or 1 needs neither a test nor an antibiotic.
• At the top, about half are streptococcal; read the higher bands as worth testing.
• In 120 Chennai children the score did no better than chance; use it to decide on testing, not instead of testing.
• Where no test exists, know both positions: IDSA tests before treating; WHO 2024 treats children in high-risk areas on suspicion.
• If you treat, give ten days of penicillin or amoxicillin, or one dose of benzathine penicillin.

For how antibiotics work and why resistance matters, see the author’s series beginning with Understanding Antibiotics (Part 1).

Declaration: the author built and maintains the tool. It is free to use. The figures in this article are those the tool carried in its Evidence tab on 5 November 2026, each from the source the tool names. The illustrative cases follow the tool’s rules; check the tool’s result for a real patient.

References

1. 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.
2. 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.
3. 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.
4. 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.
5. World Health Organization. WHO Guideline on the Prevention and Diagnosis of Rheumatic Fever and Rheumatic Heart Disease. Geneva: WHO; 2024.
6. Saxena A, Kaur K. Rheumatic fever and rheumatic heart disease in Indian children: setting priorities in the current decade. Indian Heart J. 2024.
7. Vasudevan J, Mannu A, Ganavi G. McIsaac Modification of Centor Score in Diagnosis of Streptococcal Pharyngitis and Antibiotic Sensitivity Pattern of Beta-hemolytic Streptococci in Chennai, India. Indian Pediatr. 2019;56(1):49-52.
8. 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.
9. Indian Council of Medical Research, Department of Health Research. Standard Treatment Workflow: Pharyngitis and Sore Throat (ICD-10 J02). New Delhi: ICMR; October 2019.
10. Working Group on Pediatric Acute Rheumatic Fever and Cardiology Chapter, Indian Academy of Pediatrics. Consensus guidelines on pediatric acute rheumatic fever and rheumatic heart disease. Indian Pediatr. 2008;45(7):565-573.