Strep Throat Test

Also Known As:
Throat Culture
Rapid Strep Test
Rapid Antigen Detection Test (RADT)
Streptococcal Screen
Group A Streptococcus (GAS)
Streptococcus (Group A) Rapid by NAAT

Formal Name:
Group A Beta Hemolytic Streptococcus Culture|Rapid Antigen Group A Streptococcus Test

This article was last modified on January 27, 2021

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Influenza Tests

At a Glance

Why Get Tested?

To determine if your sore throat is strep throat, an infection caused by group A streptococcus (GAS) bacteria

When To Get Tested?

When you have a sore throat that starts quickly and lasts more than a week and/or you have other symptoms, such as a fever of 101° F or higher or reddened throat and/or tonsils with white or yellow patches or streaks

Sample Required?

A health care practitioner uses a tongue depressor to hold down your tongue and then inserts a swab into your mouth and rubs it against the back of your 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 may be used to perform a throat culture as a follow-up test, when necessary.

Test Preparation Needed?

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

What is being tested?

The bacteria Streptococcus pyogenes, also known as group A beta-hemolytic streptococcus or group A strep (GAS), causes strep throat, the most common bacterial cause of inflammation and soreness of the back of the throat (pharyngitis). Strep tests include rapid strep tests and throat cultures that detect these bacteria in a sample taken from the back of your throat.

While most sore throats are caused by a virus and will resolve without treatment within a few days, some people with sore throats have strep throat. Strep throat is most common in children and teens ages 5 to 15 years old. It is important to diagnose and treat strep infections promptly with antibiotics because they are very contagious and complications can develop.

Strep throat can easily spread when an infected person coughs or sneezes and other people come into contact with the droplets or mucus. Touching your face, eyes or mouth after touching something that has these droplets on it can spread the infection. The best way to avoid getting strep throat is to wash your hands thoroughly and often and avoid sharing items like utensils or cups. If you have a sore throat, you should wash your hands often and cover your mouth with a tissue or sleeve when coughing and sneezing.
If strep throat is not diagnosed and treated, complications may develop, especially in children. These complications may include rheumatic fever, which can damage the heart, and glomerulonephritis, which affects the kidneys. Because strep infections are routinely diagnosed and treated, these complications are rare in the United States now, but they do still occur.

A rapid strep test and/or a throat culture is used to diagnose group A strep as the cause of symptoms so your health care practitioner can prescribe the proper antibiotics for treatment.

Common Questions

How is the test used?

Strep tests are used to determine whether your sore throat is strep throat, an infection of the throat and tonsils caused by group A strep (GAS).

Rapid strep tests—a rapid antigen detection test (RADT) can be used to detect group A strep proteins (antigens). Results are typically available in 10-20 minutes. Molecular tests can detect genetic material from group A strep bacteria in throat swab specimens in less than 8 minutes. If the results of the rapid test are positive, further testing is not needed and treatment with an antibiotic can be started right away.
Throat culture—if the rapid strep test is negative, and your healthcare practitioner still suspects strep, a throat culture may be performed. A culture will likely be done for children or teens to confirm the results and avoid missing infections that could lead to serious complications, such as rheumatic fever. A throat culture is more sensitive than the rapid strep test, but it may take 24-48 hours for results.

When is it ordered?

A health care practitioner will typically order a strep test when you have a sore throat and other symptoms that suggest strep throat. There is a higher suspicion of strep in children with sore throats and when you have been in close contact with someone who has been diagnosed with strep throat. You or your child should see a healthcare provider and get tested when you have signs and symptoms such as:

Sore throat that starts quickly and lasts more than a week, or recurrent sore throats
Fever of 101° F or higher
Reddened (inflamed) throat and/or tonsils with white or yellow patches or streaks
Tiny red spots at the back of the roof of the mouth
Difficulty or severe pain when swallowing
Headache, body aches
Nausea or vomiting
Tender and/or swollen throat or lymph nodes
Rash
Hoarseness lasting more than two weeks
Blood in saliva or mucus
Excessive drooling in young children
Symptoms of dehydration, such as excessive thirst, dry mouth, decreased urination

Testing may not be done when you also have symptoms more closely associated with a viral infection, such as:

Cough
Runny nose
Mouth sores

What does the test result mean?

A positive rapid strep test means you have strep throat.
A negative rapid test indicates that you probably do not have strep throat. However, a throat culture may be performed to confirm the results if your healthcare provider still suspects strep, especially among children and teens.
A throat culture that is positive for group A strep means you have strep throat.
A throat culture that is negative means it is most likely that the sore throat is due to a viral infection that will resolve on its own.

How long does antibiotic treatment for strep throat usually last?

Treatment lasts about 10 to 14 days, depending on the antibiotic prescribed. Although your symptoms may improve or disappear before you have taken all of your antibiotics, you should complete your full course of treatment by taking all of the pills that were prescribed.

How long should I stay away from other people if I have a positive test result?

You should complete at least 24 hours of antibiotics before close contact with others.

When can my child go back to school?

Usually after one full day of therapy and absence of significant fever, your child could return to school. However, a few small studies have found that children may return to school as soon as 12 hours after taking their first dose of antibiotic provided they no longer have a fever and their symptoms have improved.

If one child in my family has strep throat, is everyone going to get sick?

Other family members, including adults, can be infected by the bacteria. Your health care provider may test all family members who have sore throats and may test children under the age of 3. In most cases, it is not necessary to test other family members who do not have symptoms.

What can I do to prevent the spread of strep throat?

You can stop the spread of strep throat by good hand washing, especially after coughing and sneezing and before preparing food or eating. If you have a sore throat, you should be seen by a healthcare provider who can perform tests to find out whether the illness is strep throat. If the test result shows strep throat, you should stay home from work, school, or daycare until 24 hours after taking an antibiotic.

I've had strep throat before and was treated with antibiotics. Can I get it again?

Yes. Although antibodies may protect those who have had previous strep infections, there are so many different strains of the bacteria that it is unlikely you will be immune to all of them. You can potentially get strep throat again and again. The best way to decrease the risk of transmission to others is to minimize close contact with others when ill and wash hands often and thoroughly with soap and water or alcohol-based hand scrub.

What is an ASO test and how is it used to detect a strep infection?

Antistreptolysin O (ASO) is a blood test used to help diagnose a current or past infection with group A strep (Streptococcus pyogenes). It detects antibodies to streptolysin O, one of the many strep antigens. This test is rarely ordered now compared to thirty years ago. For an acute strep throat infection, the ASO test is not helpful; the rapid strep test or throat culture should be used. However, if a health care practitioner is trying to find out if someone had a recent strep infection that may not have been diagnosed, this test could be helpful. In addition, it may be used to help diagnose rheumatic fever or glomerulonephritis, which occurs weeks after a strep throat infection when the rapid strep and throat culture would no longer be positive.

Do other group A strep cause other types of infections?

Yes. Group A strep can also cause infections such as impetigo and, rarely, more serious conditions such as toxic shock syndrome or necrotizing fasciitis (the so-called “flesh-eating bacteria”).

Are there other types of strep bacteria that can cause a sore throat?

Group C and group G strep, normally found in animals, can rarely cause sore throats in humans. However, these bacteria do not pose a risk for the serious secondary complications associated with group A strep. Antibiotic treatment for group A strep will be effective against these bacteria as well.

Is there anything else I should know?

During influenza season, the early symptoms of influenza, such as fever, chills, headache, sore throat, and muscle pain, may mimic strep throat. To differentiate between strep and influenza, a rapid strep test and a rapid influenza test may be done at the same time.

Most people with strep throat would eventually recover without antibiotic treatment, but they would be contagious for a longer period of time and are at a greater risk of developing secondary complications.

Strep throat is most common in children and teens ages 5 to 15. Some school children may be carriers, people who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.

Recent antibiotic therapy or gargling with some mouthwashes may affect the rapid strep test results.

Related Images

Group A streptococcus bacteria on human white blood cell. Group A strep causes strep throat. Image credit: National Institute of Allergies and Infectious Diseaes

View Sources

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