The different types of tests for Group B Strep Carriage.
Make sure you take the right test.
The UK currently does not offer routine antenatal testing for Group B Strep. This is in sharp contrast to many other developed countries who provide GBS, Strep B screening to all pregnant women. Some women in the UK are offered a Group B Strep test if GBS was detected in a previous pregnancy.
The NHS commonly use two tests to detect Group B Strep carriage; a standard ‘non-selective’ swab test, known as the High Vaginal Swab (HVS) test and a Group B Strep-specific swab test, known as the Enriched Culture Medium (ECM) test.
The High Vaginal Swab (HVS) test is used when a woman has vaginal symptoms needing further investigation and is a general-purpose test. A swab is used to take a sample from high up in the vagina which is then processed on an agar plate in a laboratory. This test is not designed to specifically detect Group B Strep and can often miss GBS bacteria.
A Positive Group B Strep High Vaginal Swab (HVS) test result is highly reliable as there are very few false-positive results. However, A Negative Group B Strep High Vaginal Swab (HVS) test result is not reliable, a high proportion of false-negative results are given finding GBS in only half of those with Strep B carriage; meaning 50% are incorrectly told that they are not a carrier.
You can rely on a Positive High Vaginal Swab (HVS) test but be aware of a Negative one.The Enriched Culture Medium (ECM) test
A negative result is 96% predictive that a woman will not be carrying Group B Strep at delivery. A small percentage of women can acquire GBS carriage between the test and giving birth.
A positive result is 87% predictive that a woman will be carrying Group B Strep at delivery. Although some women do lose carriage between taking the test and giving birth.
The countries which test all pregnant women for Strep B use the Enriched Culture Medium (ECM) test usually at 35-37 weeks of pregnancy.
Health services in the UK currently rely upon a ‘risk factor’ approach to determine which newborns are more likely to be at-risk of developing a GBS infection during birth. The approach looks at factors such as high temperature during labour, labour starting preterm, waters breaking early or a previous GBS baby. A small group of women who carried Group B Strep in a previous pregnancy where their baby did not develop a GBS infection do qualify to be offered an ECM test through the NHS.
Most pregnant women that want to be tested for Group B Strep carriage during their pregnancy buy a private test.
Urine tests offered during pregnancy. An initial dipstick test may signal the presence of infection and that further investigation is needed. But Group B Strep cannot be detected by a urine dipstick test unless cultured in a laboratory from a urine sample. The level of bacteria found and whether the woman shows any symptoms, may indicate a Group B Strep urinary tract infection (UTI) which will need treating with antibiotic tablets.
A negative urine test after culture only means that Group B Strep has not been found in the urine. GBS, Strep B could still be present in the vagina or rectum. There are currently some clinical research trials in the UK looking at whether a Rapid or ‘bedside’ test or ‘point-of-care’ test, is a good way of determining which women carry Group B Strep. Samples are taken from both the low vagina and rectum using swabs, which are processed in a machine usually on the labour ward.
Private Group B Strep, Strep B tests are available in the UK. Our test is safe, accurate, reliable and also extremely convenient as it is a Home-to-Laboratory test.