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Strep Throat Test

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Also known as: Throat Culture; Culture, Throat; Rapid Strep Test; Streptococcal Screen
Formal name: Group A streptococcus (GAS); Group A beta hemolytic streptococcus

The Test Sample

What is being tested?

The bacterium Streptococcus pyogenes, also known as group A beta-hemolytic streptococcus or group A streptococcus (GAS), causes "strep throat," the most common bacterial cause of inflammation and soreness of the back of the throat (pharyngitis). Strep throat tests identify the presence of this bacterium as the cause of a sore throat.

While most sore throats are caused by a virus and will resolve without treatment within a few days, 5-15% of adults and 20-30% of children with sore throats have strep throat. It is important that these bacterial strep infections be promptly identified and treated with antibiotics. Strep throat is contagious and can spread to close contacts. If the infection is not treated, secondary complications may develop, especially in children. These complications may include rheumatic fever, which can damage the heart, and glomerulonephritis, which affects the kidneys. Because streptococcal infections are routinely diagnosed and treated, these complications have become much rarer in the United States, but they do still occur.

Symptoms of strep throat vary and can be similar to those caused by other infections. They may include:

  • Sore throat
  • Fever
  • Headache
  • Reddened (inflamed) throat with or without white or yellow spots
  • A swollen, tender neck
  • Weakness
  • Loss of appetite

A rapid strep test and/or a throat culture is used to diagnose group A streptococci as the cause of these symptoms and allows the doctor to prescribe the proper antibiotics for treatment.

How is the sample collected for testing?

A doctor, nurse, or other health care professional uses a tongue depressor to hold down a person's tongue and then inserts a special swab into the mouth and rubs it against the back of the throat and tonsils. The swab may be used to do a rapid strep test in a doctor's office or clinic, or it may be sent to a laboratory. A second swab may be collected along with the first one. This extra sample is used to perform a throat culture as a follow-up test, when necessary.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed. The test should be performed before antibiotics are prescribed.