Also Known As
Throat culture
Formal Name
Group A streptococcus
Group A beta haemolytic streptococcus
Streptococcus pyogenes
This article was last reviewed on
This article waslast modified on 14 March 2023.
At a Glance
Why Get Tested?

To diagnose a possible bacterial infection of the throat (usually Streptococcus pyogenes)

When To Get Tested?

If you have a sore throat and fever and your doctor thinks it may have a bacterial cause (although most sore throats are caused by viruses and won't require antibiotics)

Sample Required?

The bacteria are tested for by throat culture. Your doctor may use a tongue depressor to hold down your tongue, and then insert a special swab into your mouth and brush it against your throat and tonsils. The swab will be sent to a laboratory, where culture is performed.

Test Preparation Needed?

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

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

The test identifies Streptococcus pyogenes, known as Group A streptococcus, which are bacteria that infect the back of the throat and are a common cause for an infected and sore throat. Whilst group A Streptococcus is the commonest bacterial cause of a severe sore throat (pharyngitis), it is not the only bacterial cause and others include group C and G Streptococcus and Arcanobacterium.

Accordion Title
Common Questions
  • How is it used?

    The majority of sore throats are caused by a virus and do not require active treatment with antibiotics. Some, caused by the Streptococcus pyogenes bacterium, may be severe and are treatable with antibiotics. Your doctor will assess you based on your symptoms and may take a throat culture to help make the correct diagnosis if they think you might have a bacterial infection of your throat. This allows your doctor to prescribe the correct antibiotics for treatment. A throat culture may take several days to provide results.

  • When is it requested?

    Your doctor may request this test if you have a sore throat and a fever that might be due to a bacterial infection. Other symptoms include:

    • tonsils that may appear red with white or yellow spots at the back of the throat
    • a swollen, tender neck
    • skin rash
    • weakness
    • loss of appetite, feeling sick
    • flu-like illness, aching body
  • What does the test result mean?

    A positive throat culture indicates the presence of group A streptococci, the bacteria that cause sore throats.

  • Is there anything else I should know?

    A sore throat due to a bacterial infection may spread through person-to-person contact. Symptoms usually occur within two to seven days after exposure. If untreated, this throat infection can create serious lifelong problems in a small minority of patients, however these complications are very rare in the UK.

    This infection is most common in 5- to 15-year-olds. Up to 20% of school children may be "carriers" - people who have the bacteria but who have no symptoms. Carriers can still spread the infection to others.

  • How long does treatment for bacterial infection of the throat usually last?

    Five to 10 days depending on which antibiotic prescribed

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

    Twenty-four hours after starting medication

  • When can my child go back to school?

    Usually after one full day of therapy and absence of significant fever.

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

    Other family members, including adults, can contract the bacteria.  They must be vigilant and seek healthcare attention if feeling unwell.

  • What is an ASO test and how is it used to detect a bacterial infection of the throat?

    Antistreptolysin O (ASO) titre 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 streptococcus antigens. This test is rarely used now compared to thirty years ago. For an acute throat infection, this test is not performed; the throat culture is used. It is because ASO may take at least a week to become positive after the infection. However, if a doctor is trying to find out if someone had a recent infection that may not have been diagnosed, this test could be helpful. In addition, it may be used to help diagnose rheumatic fever, which occurs weeks after a bacterial throat infection when the throat culture would no longer be positive.