URL of this page: https://medlineplus.gov/lab-tests/strep-a-test/

Strep A Test

What is a strep A test?

Strep A, also known as group A strep, is a type of bacteria that causes strep throat and other infections. Strep throat is an infection that affects the throat and tonsils. The infection is spread from person to person through coughing or sneezing. While you can get strep throat at any age, it's most common in children 5 to 15 years old.

Strep throat can be easily treated with antibiotics. But left untreated, strep throat can lead to serious complications. These include rheumatic fever, a disease that can damage the heart and joints, and glomerulonephritis, a type of kidney disease.

Strep A tests check for strep A infections. There are two types of strep A tests:

  • Rapid strep test. This test looks for antigens to strep A. Antigens are substances that cause an immune response. A rapid strep test can provide results in 10–20 minutes. If a rapid test is negative, but your provider thinks you or your child has strep throat, he or she may order a throat culture.
  • Throat culture. This test looks for strep A bacteria. It provides a more accurate diagnosis than a rapid test, but it can take 24–48 hours to get results.

Other names: strep throat test, throat culture, group A streptococcus (GAS) throat culture, rapid strep test, streptococcus pyogenes

What is it used for?

A strep A test is most often used to find out if a sore throat and other symptoms are being caused by strep throat or by a viral infection. Strep throat needs to be treated with antibiotics to prevent complications. Most sore throats are caused by viruses. Antibiotics don't work on viral infections. Viral sore throats usually go away on their own.

Why do I need a strep A test?

Your health care provider may order a strep A test if you or your child has symptoms of strep throat. These include:

  • A sudden and severe sore throat
  • Pain or difficulty swallowing
  • Fever of 101° or more
  • Swollen lymph nodes

Your provider may also order a strep A test if you or your child has a rough, red rash that starts on the face and spreads to another part of the body. This type of rash is a sign of scarlet fever, an illness that can happen a few days after you've been infected with strep A. Like strep throat, scarlet fever is easily treated with antibiotics.

If you have symptoms such as a cough or runny nose along with your sore throat, it's more likely that you have a viral infection rather than strep throat.

What happens during a strep A test?

A rapid test and a throat culture are done in the same way. During the procedure:

  • You will be asked to tilt your head back and open your mouth as wide as possible.
  • Your health care provider will use a tongue depressor to hold down your tongue.
  • He or she will use a special swab to take a sample from the back of your throat and tonsils.
  • The sample may be used to do a rapid strep test in the provider's office. Sometimes the sample is sent to a lab.
  • Your provider may take a second sample and send it to a lab for a throat culture if necessary.

Will I need to do anything to prepare for the test?

You don't any special preparations for a rapid strep test or a throat culture.

Are there any risks to the test?

There is no risk to having swab tests, but they may cause slight discomfort and/or gagging.

What do the results mean?

If you or your child has a positive result on a rapid strep test, it means you have strep throat or another strep A infection. No further testing will be needed.

If the rapid test was negative, but the provider thinks you or your child might have strep throat, he or she may order a throat culture. If you or your child has not already provided a sample, you will get another swab test.

If the throat culture was positive, it means you or your child has strep throat or other strep infection.

If the throat culture was negative, it means your symptoms are not being caused by strep A bacteria. Your provider will probably order more tests to help make a diagnosis.

If you or your child was diagnosed with strep throat, you will need to take antibiotics for 10 to 14 days. After a day or two of taking the medicine, you or your child should start to feel better. Most people are no longer contagious after taking antibiotics for 24 hours. But it's important to take all the medicine as prescribed. Stopping early can lead to rheumatic fever or other serious complications.

If you have questions about your results or your child's results, talk to your health care provider.

Is there anything else I need to know about a strep A test?

Strep A can cause other infections besides strep throat. These infections are less common than strep throat but are often more serious. They include toxic shock syndrome and necrotizing fasciitis, also known as flesh-eating bacteria.

There are also other kinds of strep bacteria. These include strep B, which can cause a dangerous infection in newborns, and streptococcus pneumoniae, which causes the most common type of pneumonia. Streptococcus pneumonia bacteria can also cause infections of the ear, sinuses, and bloodstream.

References

  1. ACOG: The American College of Obstetricians and Gynecologists [Internet]. Washington D.C.: American College of Obstetricians and Gynecologists; c2019. Group B Strep and Pregnancy; 2019 Jul [cited 2019 Nov 19]; [about 3 screens]. Available from: https://www.acog.org/Patients/FAQs/Group-B-Strep-and-Pregnancy
  2. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Group A Streptococcal (GAS) Disease; [cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.cdc.gov/groupastrep/index.html
  3. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Group A Streptococcal (GAS) Disease: Rheumatic Fever: All You Need to Know; [cited 2019 Nov 19]; [about 4 screens]. Available from: https://www.cdc.gov/groupastrep/diseases-public/rheumatic-fever.html
  4. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Group A Streptococcal (GAS) Disease: Strep Throat: All You Need to Know; [cited 2019 Nov 19]; [about 4 screens]. Available from: https://www.cdc.gov/groupastrep/diseases-public/strep-throat.html
  5. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Streptococcus Laboratory: Streptococcus pneumoniae; [cited 2019 Nov 19]; [about 3 screens]. Available from: https://www.cdc.gov/streplab/pneumococcus/index.html
  6. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2019. Strep Throat: Overview; [cited 2019 Nov 19]; [about 3 screens]. Available from: https://my.clevelandclinic.org/health/diseases/4602-strep-throat
  7. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2019. Strep Throat Test; [updated 2019 May 10; cited 2019 Nov 19]; [about 2 screens]. Available from: https://labtestsonline.org/tests/strep-throat-test
  8. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2019. Strep Throat: Diagnosis and treatment; 2018 Sep 28 [cited 2019 Nov 19]; [about 4 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/strep-throat/diagnosis-treatment/drc-20350344
  9. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2019. Strep Throat: Symptoms and causes; 2018 Sep 28 [cited 2019 Nov 19]; [about 3 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/strep-throat/symptoms-causes/syc-20350338
  10. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2019. Streptococcal Infections; [updated 2019 Jun; cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/infections/bacterial-infections-gram-positive-bacteria/streptococcal-infections
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2019. Health Encyclopedia: Beta Hemolytic Streptococcus Culture (Throat); [cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=beta_hemolytic_streptococcus_culture
  12. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2019. Health Encyclopedia: Pneumonia; [cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P01321
  13. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2019. Health Encyclopedia: Strep Screen (Rapid); [cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=rapid_strep_screen
  14. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2019. Health Information: Strep Throat: Exams and Tests; [updated 2018 Oct 21; cited 2019 Nov 19]; [about 9 screens]. Available from: https://www.uwhealth.org/health/topic/major/strep-throat/hw54745.html#hw54862
  15. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2019. Health Information: Strep Throat: Topic Overview; [updated 2018 Oct 21; cited 2019 Nov 19]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/major/strep-throat/hw54745.html
  16. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2019. Health Information: Throat Culture: How It Is Done; [updated 2019 Mar 28; cited 2019 Nov 19]; [about 5 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/throat-culture/hw204006.html#hw204012
  17. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2019. Health Information: Throat Culture: Why It Is Done; [updated 2019 Mar 28; cited 2019 Nov 19]; [about 3 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/throat-culture/hw204006.html#hw204010

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.