Group B Strep (GBS) Test
Reviewed
A group B strep test checks for GBS bacteria in the body. Many healthy people carry GBS without symptoms, but it can cause serious infections in newborns, older adults, and people with weakened immune systems. In pregnant women, testing is done between 36 and 38 weeks to guide antibiotic use during labor and prevent transmission to the baby.
Preparation and collection
No special preparations needed.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- GBS bacteria can grow back quickly after antibiotics, so treatment earlier in pregnancy is not effective.
- In newborns, early-onset GBS disease symptoms usually appear on the day of birth; late-onset can appear between 7 and 89 days of life, and the source is unknown.
- If your provider suspects a GBS infection, treatment may begin before test results are available because GBS can cause serious illness or death.
What to do next
If you are pregnant and test positive, you will receive IV antibiotics during labor. If your baby tests positive, they will be treated with antibiotics. Discuss any questions about your or your baby's results with your healthcare provider.