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Beta Hemolytic Streptococcus Culture (Genital, Urine)

Does this test have other names?

Group B strep screen

What is this test?

This test looks for group B streptococcus (GBS) bacteria in a culture sample either from your urine or from secretions in your vagina and rectum.

GBS bacteria live in your digestive tract and vagina without causing health problems. But they can cause severe illness in pregnant women and newborns. The bacteria are called hemolytic because they can break down red blood cells.

A GBS infection makes it more likely that you will deliver preterm. Your amniotic fluid may also be infected, and your uterus will also be more likely to be infected with GBS after delivery.

GBS can infect your baby and cause serious problems, including pneumonia; septicemia, or blood poisoning; and meningitis, an inflammation of the lining of the brain and spinal cord.

You can develop a GBS infection even if you're not pregnant. You're at risk for this infection if you have diabetes, cancer, HIV, or severe liver or kidney disease. You're also at greater risk if you are dependent on alcohol, have heart disease, or are an older adult.

Why do I need this test?

You may have this test as part of routine prenatal care. You may also have this test if you have symptoms of GBS infection during pregnancy. Symptoms include:

  • Pain

  • Frequent urination

  • Blood in your urine

Your doctor will likely do a urine culture early in your pregnancy to look for a bladder infection. If GBS or other bacteria appear in your urine, your doctor may give you antibiotics to clear up the infection.

You will likely have a GBS genital culture done between weeks 35 and 37 of your pregnancy. If your test is positive, you may be treated with antibiotics to get rid of the infection. If your baby is born with a GBS infection, he or she will be treated with antibiotics, as well.

You may also have this test even if you aren't pregnant if your doctor suspects that you have one of these conditions:

  • Bacteremia, which happens when bacteria invade your bloodstream

  • Sepsis, or blood-poisoning, a life-threatening inflammation of your entire body

  • Soft tissue infection

What other tests might I have along with this test?

Your doctor may also order a Gram stain.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal results for either a urine or genital culture are negative, meaning that you don't have GBS bacteria.

Positive results mean that the bacteria were found in the culture and that you likely have a GBS infection.

How is this test done?

The urine culture test requires a urine sample.

The genital culture requires a sample from your vagina and rectum. Your doctor will take the sample by gently swabbing these areas with a cotton swab.

Does this test pose any risks?

The swab might cause slight discomfort. The urine test poses no known risks.

What might affect my test results?

Other factors aren't likely to affect your results.

How do I get ready for this test?

You don't need to prepare for this test.  But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.