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Strep B Test

What is a group B strep test?

Strep B, also known as group B strep (GBS), is a type of bacteria commonly found in the digestive tract, urinary tract, and genital area. Many healthy people have GBS bacteria in their bodies.

Most of the time, GBS bacteria are not harmful and do not make people feel sick or have any symptoms. But in rare cases, these bacteria cause certain infections, known as GBS disease. This is more likely in people who are age 65 and older, have certain chronic health problems, or have a condition that weakens their immune system. And sometimes GBS infections can be very serious, or even life-threatening, in newborns.

In most cases, it is not known how people spread GBS bacteria to others. However, it is known that pregnant people can pass the bacteria to their babies during a vaginal delivery. GBS is usually found in the vagina and rectum, so. the baby can be exposed to the GBS bacteria during labor. It is rare, but it can cause serious illness in the baby.

There are two types of GBS infections in babies. The types are based on the age of the infant when signs and symptoms begin to show:

  • In early-onset GBS disease, the signs and symptoms start during the first six days of life
  • In late-onset GBS disease, the signs and symptoms start during between 7 to 89 days of life. The source of late-onset GBS infection is unknown.

In newborns, GBS can cause:

  • Bacteremia (infection in the bloodstream)
  • Pneumonia (inflammation of the lung)
  • Meningitis (inflammation of the thin tissue that surrounds the brain and spinal cord)
  • Other serious illnesses

GBS bacteria are a leading cause of meningitis and bloodstream infections in a newborn's first three months of life.

In pregnant people, GBS can cause:

  • Bacteremia
  • Chorioamnionitis (infection of the placenta and amniotic fluid)
  • Endometritis (infection of the membrane lining the uterus)
  • Urinary tract infections

In older adults and people with chronic health conditions, GBS bacteria can cause:

  • Bacteremia
  • Urinary tract infection
  • Pneumonia
  • Bone and joint infections
  • Endocarditis (infection of the heart valves)
  • Meningitis
  • Skin or soft-tissue infections

A group B strep test checks for GBS bacteria. If the test shows that a pregnant person has GBS, taking antibiotics during labor can protect the baby from infection.

Other names: group B streptococcus, group B beta-hemolytic streptococcus, Streptococcus agalactiae, beta-hemolytic strep culture

What is it used for?

A group B strep test is most often used to look for GBS bacteria in pregnant people. Most pregnant people are tested as part of routine prenatal screening. It may also be used to test infants who show signs of infection.

Why do I need a group B strep test?

You may need a strep B test if you are pregnant. The American College of Obstetricians and Gynecologists recommends GBS testing for all pregnant people. Testing is usually done between 36 and 38 weeks of pregnancy. If you go into labor earlier than 36 weeks, you may be tested at that time.

Symptoms depend on the part of the body that is infected. Symptoms of GBS disease are different in newborns compared to people of other ages who get GBS disease. Most newborns who get sick in the first week of life (early onset) have symptoms on the day of birth. In contrast, babies who develop disease later (late onset) can appear healthy at birth and during their first week of life.

A baby may need a group B strep test if he or she has symptoms of infection. These include:

  • High fever
  • Trouble with feeding
  • Trouble breathing
  • Lack of energy (hard to wake up)
  • Irritability
  • Blue-ish skin color
  • Unstable blood pressure (a pattern where the blood pressure suddenly spikes and then falls back to normal)
  • Kidney problems

Pregnant people usually do not feel sick or have any symptoms. In adults, symptoms depend on the infection caused by GBS.

Symptoms of bacteremia include:

  • Fever
  • Chills
  • Low alertness

Symptoms of pneumonia include:

Skin and soft tissue infections often appear as a bump or infected area on the skin that may be:

  • Red
  • Swollen or painful
  • Warm to the touch
  • Full of pus or other drainage
  • Fever, in some cases

Bone and joint infections often appear as pain in the infected area and might also include:

  • Fever
  • Chills
  • Swelling
  • Stiffness or being unable to move the affected joint(s)

What happens during a group B strep test?

If you are pregnant, your health care provider may order a swab test or a urine test.

For a swab test, you will lie on your back on an exam table. Your provider will use a small cotton swab to take a sample of cells and fluids from your vagina and rectum.

For a urine test, a health care professional may give you a cleansing wipe, a small container, and instructions for how to use the "clean catch" method to collect your urine sample. It's important to follow these instructions so that germs from your skin don't get into the sample:

  • Wash your hands with soap and water and dry them.
  • Open the container without touching the inside.
  • Clean your genital area with the cleansing wipe:
  • For a penis, wipe the entire head (end) of the penis. If you have a foreskin, pull it back first.
  • For a vagina, separate the labia (the folds of skin around the vagina) and wipe the inner sides from front to back.
  • Urinate into the toilet for a few seconds and then stop the flow. Start urinating again, this time into the container. Don't let the container touch your body.
  • Collect at least an ounce or two of urine into the container. The container should have markings to show how much urine is needed.
  • Finish urinating into the toilet.
  • Put the cap on the container and return it as instructed.

If your baby needs testing, a provider may do a blood test or a lumbar puncture (spinal tap).

For a blood test, a health care professional will use a small needle to take a blood sample from your baby's heel. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. Your baby may feel a little sting when the needle goes in or out.

A lumbar puncture, also known as a spinal tap, is a test that collects and looks at spinal fluid, the clear liquid that surrounds the brain and spinal cord. During the procedure:

  • A nurse or other provider will hold your baby in a curled-up position.
  • A provider will clean your baby's back and inject an anesthetic into the skin, so your baby won't feel pain during the procedure. The provider may put a numbing cream on your baby's back before this injection.
  • The provider may also give your baby a sedative and/or pain reliever to help him or her better tolerate the procedure.
  • Once the area on the back is completely numb, your provider will insert a thin, hollow needle between two vertebrae in the lower spine. Vertebrae are the small backbones that make up the spine.
  • The provider will withdraw a small amount of cerebrospinal fluid for testing. This will take about five minutes.

The provider may also order a chest X-ray to help determine if someone has GBS disease.

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

You don't any special preparations for group B strep tests.

Are there any risks to the test?

There is no risk to you from a swab or urine test. Your baby may have slight pain or bruising after a blood test, but that should go away quickly. Your baby will likely feel some pain after a spinal tap, but that shouldn't last too long. There is also a small risk of infection or bleeding after a lumbar puncture.

What do the results mean?

If you are pregnant and results show you have GBS bacteria, you will be given antibiotics intravenously (by IV) during labor, at least four hours before delivery. This will prevent you from passing the bacteria to your baby. Taking antibiotics earlier in your pregnancy is not effective, because the bacteria can grow back very quickly. It's also more effective to take antibiotics through your vein (by IV), rather than by mouth.

You may not need antibiotics if you are having a planned cesarean delivery (C-section). During a cesarean delivery, a baby is delivered through the mother's abdomen rather than vaginally. But you still should be tested during pregnancy because you may go into labor before your scheduled cesarean delivery.

If your baby's results show a GBS infection, he or she will be treated with antibiotics. If your provider suspects a GBS infection, he or she may treat your baby before test results are available. This is because GBS can cause serious illness or death.

If you have questions about your results or your baby's results, talk to your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

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

Strep B is one type of strep bacteria. Other forms of strep cause different types of infections. These include strep A, which causes strep throat, and Streptococcus pneumoniae, which causes the most common type of pneumonia. Streptococcus pneumonia bacteria can also cause infections of the ear, sinuses, and bloodstream.


  1. ACOG: The American College of Obstetricians and Gynecologists [Internet]. Washington D.C.: American College of Obstetricians and Gynecologists; c2023. Group B Strep and Pregnancy; [reviewed 2021 Jul; cited 2023 Aug 28]; [about 5 screens]. Available from:
  2. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; About Group B Strep Disease; [reviewed 2022 Oct 18; cited 2023 Sep 26]; [about 2 screens]. Available from:
  3. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Preventing Group B Strep Disease in Newborns; [reviewed 2022 Oct 18; cited 2023 Aug 28]; [about 2 screens]. Available from:
  4. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Streptococcus Laboratory: Streptococcus pneumoniae; [reviewed 2021 Jul 23; cited 2023 Aug 28]; [about 1 screen]. Available from:
  5. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Symptoms of Group B Strep Disease; [reviewed 2022 Oct 18; cited 2023 Aug 28]; [about 2 screens]. Available from:
  6. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Travelers' Health: Pneumococcal Disease; [reviewed 2022 Sep 16; cited 2023 Aug 28]; [about 2 screens]. Available from:
  7. Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2023. Blood Tests; [reviewed 2022 Dec 06; cited 2023 Sep 29]; [about 16 screens]. Available from:
  8. Intermountain Healthcare: Primary Children's Hospital [Internet]. Salt Lake City: Intermountain Healthcare; c2006-2017. Lumbar Puncture in a Newborn; [reviewed 2017 Sep; cited 2023 Aug 28]; [about 2 screens]. Available from:
  9. Michigan Medicine: University of Michigan [Internet]. Ann Arbor (MI): Regents of the University of Michigan; c1995-2023. Group B Streptococcal Infections in Newborns; [cited 2023 Aug 28]; [about 4 screens]. Available from:
  10. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: meningitis; [cited 2023 Sep 25]; [about 1 screen]. Available from:
  11. Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2023. Getting a Blood Test; [reviewed 2021 Sep; cited 2023 Sep 29]; [about 4 screens]. Available from:
  12. [Internet]. Seattle (WA): OneCare Media; c2023. Blood Culture; [modified 2022 Feb 11; cited 2023 Aug 28]; [about 11 screens]. Available from:
  13. [Internet]. Seattle (WA): OneCare Media; c2023. Prenatal Group B Strep (GBS) Screening; [modified 2021 Nov 9; cited 2023 Aug 28]; [about 10 screens]. Available from:
  14. [Internet]. Seattle (WA): OneCare Media; c2023. Urine Culture Test; [modified 2022 Sep 29; cited 2023 Aug 28]; [about 10 screens]. Available from:
  15. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy [Internet]. Geneva (SUI): World Health Organization; c2010. 6. Paediatric and neonatal blood sampling; [cited 1012 Aug 28]; [about 3 screens]. Available from:

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.