How is strep throat diagnosed?

Dr. Diana K. Blythe, MD

Strep throat is diagnosed by a swab of the throat. A rapid strep test is performed on this swab. While it is a great test which is very quick, it can miss some cases of strep throat.

When a rapid test is negative, a second swab is wiped across a plate of bacteria food and then placed in a warmer. This makes a perfect environment for the bacteria to grow and is called a bacterial culture. This culture plate is looked at under the microscope each day for two days to see if the strep bacteria grows.

By using the combination of the rapid test and the culture, you get a possibility of a quick result with the back up assurance of the culture for negative rapid tests.

Strep throat is an infection in the throat and tonsils caused by group A Streptococcus bacteria (called "group A strep"). A strep test (a quick swab of the throat) can quickly show if group A strep bacteria are causing a sore throat. A test is needed to tell if you have strep throat; just looking at your throat is not enough to make a diagnosis. If the test is positive, your doctor can prescribe antibiotics. If the strep test is negative, but your doctor still strongly suspects you have this infection, a culture of your throat (another sample) may be taken as another way to test for the bacteria.

Dr. Jennifer F. Logan, MD
Family Practitioner

Diagnosis of strep throat is generally based on its course and symptoms. A doctor may decide to do a throat swab to confirm the diagnosis, although this is not always necessary. Depending on symptoms, the doctor may also choose to do a nasal swab to test for influenza, as well as a blood test for mononucleosis.

To diagnose strep throat, your doctor will look at your throat and tonsils to see if the tonsils are swollen and to study the color of the throat. You will be asked about other symptoms. For instance, if you have a cough and typical cold symptoms, you most likely don't have strep throat. But if you have a fever and maybe a rash or vomiting, you might.

To confirm the diagnosis, your doctor will swab the throat to get a sample to be tested for the presence of the streptococcus group A bacteria. The test may be considered a "throat culture" if the lab allows the bacteria to grow (which may take a few days). Your doctor may also do a rapid step test. Thid test will give you results sooner than a culture, but it may not be 100 percent accurate regarding the presence of a bacterial infection.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.