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.

This test is recommended for all pregnant women. 

GBS bacteria 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. These include pneumonia, blood poisoning (septicemia), and an inflammation of the lining of the brain and spinal cord (meningitis). GBS is most often the cause of septicemia in newborns in the U.S.

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 need this test as part of your 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 healthcare provider 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 healthcare provider 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 healthcare provider suspects that you have one of these conditions:

• Bacteremia, which happens when bacteria invade your bloodstream

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

• Soft tissue infection

What other tests might I have along with this test?

Your healthcare provider may also order a Gram stain.

What do my test results mean?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

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 is done with a urine sample.

The genital culture is done with a sample from your vagina and rectum. Your healthcare provider 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. Be sure your healthcare provider 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.