Strep throat is diagnosed from your medical history, a physical exam of your throat, and a lab test, such as a throat culture. Sometimes a rapid strep test is used to check for strep. Your doctor may confirm the results of the rapid strep test with a throat culture.
Current treatment guidelines recommend that your doctor confirm strep throat with a lab test, such as a throat culture, and not diagnose strep throat just from your symptoms. But your doctor may begin treatment for strep throat before the result of your throat culture is back if you have three or four of the following symptoms:
- A recent fever of 101°F (38.3°C) or higher
- White or yellow spots or coating on the throat or tonsils
- Swollen or tender lymph nodes on the neck
- Absence of signs of a cold or upper respiratory infection, such as coughing or sneezing
One or both of the following tests are used to confirm that you have strep throat.
- Rapid strep test analyzes the bacteria in your throat to see if strep is the cause of your sore throat. The doctor uses a cotton swab to gather cells from the back of your throat for testing.
- Throat culture is a test to find germs (such as strep bacteria) that can cause an infection. A sample of cells from the back of your throat is added to a substance that promotes the growth of bacteria. If no bacteria grow, the culture is negative. If strep bacteria grow, the culture is positive.
If symptoms of strep throat are present, it is important to be tested for strep infection. Prompt treatment will reduce the spread of strep throat and may reduce the risk of complications, such as the infection spreading to other parts of your body causing ear or sinus infections or an abscess behind or around your tonsils (peritonsillar abscess).
If you need to be tested for strep throat, the choice between a rapid strep test and a throat culture may not be clear. It may help to discuss with your doctor the advantages and disadvantages of each test. For instance, results from a rapid strep test are available within 10 to 15 minutes, and results from a throat culture may take 1 to 2 days. A throat culture is more accurate.
- A negative rapid strep test result can mean there are no strep bacteria present. But the rapid strep test can give negative results even when strep bacteria are present (false-negative test results). If the rapid strep test result is negative but strep throat is still suspected, your doctor may order a throat culture to verify the results.
- If the rapid strep test result is positive, a throat culture isn't needed. Antibiotic treatment can be started right away. Antibiotics may not make you well faster. But they shorten the time you are able to spread the disease to others. Antibiotics also lower the risk of spreading the infection to other parts of your body.
Testing is not needed:
- After antibiotic treatment, unless you still have symptoms. Testing may be done if symptoms return or you have had rheumatic fever and are at risk for it coming back.
- For a person who was exposed to strep but has no symptoms. For instance, family members of a person who has strep throat do not need to be tested unless they start to have symptoms.
It is possible for a person to carry the strep bacteria and not have any symptoms. If a number of infections occur in the same family, or if there have been severe complications such as rheumatic fever or toxic shock syndrome, it may be helpful to test family members to learn whether they are carriers of strep infection. But it is unusual for a person to catch strep throat from a carrier.