New guidelines on diagnosing strep throat advise clinicians to use a scoring system to help determine which patients should be tested for group A streptococcal pharyngitis.

The clinical practice guidelines, published by the Infectious Diseases Society of America, state evidence shows the Centor and McIsaac scoring systems marginally outperform clinical judgment in accurately diagnosing strep throat.

Until now, a clear standard in clinical practice for determining who to test for strep has not existed, said Miriam Barshak, MD, associate professor of medicine at Harvard Medical School, Boston, and author of the guidelines.

“This means that some providers are essentially testing everyone who comes in with a sore throat, while others are using some degree of clinical judgment that may be biased in ways that may lead to either overtesting or undertesting — more likely overtesting, which may lead to higher costs of care and overtreatment, since testing is imperfect,” she said.

The updated guidance aims to reduce unnecessary testing in low-risk patients, particularly when false positives can result in overdiagnosis and inappropriate prescribing of antibiotics, Barshak and her colleagues wrote.

Appropriate treatment of true cases is important both for decreasing risks for potentially severe sequelae and for the economic benefits of reducing absenteeism from work and school, Barshak and her colleagues wrote. But downsides of overtreatment include adverse effects of antibiotics and the promotion of antimicrobial resistance.

“The vast majority of people with sore throat have a viral infection, which doesn’t respond to antibiotics,” said William Schaffner, MD, professor of preventive medicine at Vanderbilt University in Nashville, Tennessee, who was not involved in the new document. “Targeting antibiotics only to the people who need them is even more important now than it was in 2012.”

Signs and symptoms of strep and other mostly viral causes of pharyngitis tend to substantially overlap, Barshak said.

“There is no single feature or even combination of features that has been found to accurately predict who has strep,” she said. “These scoring systems are actually most helpful in identifying people who are very unlikely to have strep and therefore unlikely to benefit from testing or treatment for strep.”

The Centor tool assigns one point for each of the following: tonsillar swelling or exudates, anterior cervical lymphadenopathy, history of fever, and absence of cough. The McIsaac system adds a point for patients aged 3-14 years and subtracts one point for those older than 45 years.

A score of 0 or 1 indicates a low likelihood of strep throat and no recommendation for testing. Clinicians should perform a rapid test or throat culture before treating patients with a score of 2. Scores 3-5 indicate testing first or treating empirically.

High-risk individuals should be strongly considered for testing even if their scores are low, the guidelines state. These individuals might include those with a history of previous rheumatic fever or symptoms suggestive of complicated local or systemic group A streptococcal pharyngitis infection.

Many clinicians are likely already familiar with scoring systems and incorporating their use into their clinical judgment, Barshak said.

“But I know from my own practice as well as my family and friends’ healthcare encounters that there are many patients who are getting tested for strep in the real world even though their scoring system results would suggest such testing is unlikely to be beneficial,” she said.

The guidelines were authored by a multidisciplinary panel of specialists from infectious diseases, pediatrics, public health, microbiology, and other fields. The panel conducted a systematic review of studies through March 2025 that looked at the reliability of using clinical scoring systems for diagnosis of group A streptococcal pharyngitis.

“There was not enough data in the literature to support a recommendation to use any particular scoring system over any other,” Barshak said.

Barshak said the guidelines “recommend a scoring system in conjunction with clinical judgment.”

The six studies they identified, published between 1977 and 2001, used throat culture as the reference standard and assessed scoring systems by Breese, McIsaac, Centor, Attia, and Fujikawa. Four studies focused only on children.

In children, scoring systems had slightly better sensitivity than clinicians and similar specificity. The only tool that assessed both children and adults was McIsaac, which had better sensitivity than clinician judgment (0.83 vs 0.69, respectively) and comparable specificity (0.94 vs 0.97).

Evidence for evaluation was only available for the Centor and McIsaac systems. A third decision-making tool, the FeverPAIN score, is included in other strep guidelines, but the panel did not find studies allowing them to assess it.

The scoring systems do not apply to children younger than 3 years because their symptoms can present differently.

“This is really designed to help the clinician focus on those individuals with a sore throat who do need antibiotic treatment, and you can give symptomatic treatment to the others,” Schaffner said. “With this checklist, you can move the likelihood that they actually have a treatable strep infection very substantially, and you can be more confident in your use of antibiotics when you treat someone with a sore throat.”

The guidelines were funded by the Infectious Diseases Society of America. Schaffner reported having no relevant disclosures. Barshak reported owning stocks and bonds in Viatris, Boston Scientific, and Danaher, and receiving royalties from UpToDate. Other authors of the guidelines reported receiving consulting, advisory, speaking, or research grants from Amgen, Biogen, Eli Lilly and Company, bioMérieux, Genetic Signatures, and others.

Tara Haelle is a science/health journalist based in Dallas.