The Importance of Strep Tests

One of the most common reasons for patients to come see us is for a sore throat. Except in extremely unusual circumstances, the only bacterial cause of throat infections in children is strep throat. That means that strep throat is the only cause of a sore throat which will be helped by treatment with antibiotics. Furthermore, strep is less common than viruses as a cause of sore throats.

There is a quick, easy test to check for strep throat that involves swabbing the throat and testing for streptococcal antigens (essentially tiny pieces of the strep bacteria). These tests catch a very high percentage of cases of strep throat. If the strep test is negative, generally a back-up throat culture is performed to pick up the ones that sneak through unidentified.

Why is this important? Because doctors are not very good at diagnosing strep throat without the test. When I was in the first year of my pediatric residency at UVa, we had a contest to see who could best predict the results of strep tests on their patients. We wrote down our predictions prior to having the tests run and then calculated who had the highest percentage correct for the year. I was the “Golden Loop” winner for my year (named for the loop used to streak a sample on a blood agar plate for growing bacteria). Even so, I think my percentage of correct predictions was only around 70%. And after 18 years of practicing pediatrics and thousands of visits in which I have done strep tests, it is still not unusual for me to be surprised by the result of a strep test.

Some providers diagnose strep throat using the Centor criteria. These criteria were developed for adults. If a patient meets all of the criteria, their chance of having strep throat is around 50%. So if adults are treated based on these criteria alone, about half of them will receive antibiotics for a condition which they do not have. When applied to children, the predictive value of these criteria is even lower.

It is not unusual for us to see patients who were seen elsewhere for a sore throat, placed on antibiotics without a strep test, and are no better a couple days later. It is understandably frustrating for them to have a second visit for the same problem only to learn they have an illness for which the treatment they were prescribed would not be expected to be helpful.

Strep tests are quick, easy, and reliable. So the next time someone wants to treat your child’s sore throat with antibiotics without first testing for strep, request a strep test. There is a good chance it could save him from taking 10 days of antibiotics which will not help and could cause side effects. In addition, you will be doing society a favor. Overuse of antibiotics leads to antibiotic resistance and, according to one recent estimate, infections with antibiotic-resistant bacteria cost the United States $20 billion annually. The first, obvious step to combating antibiotic resistance and doing what’s best for patients, is to not use antibiotics for conditions they will not help.