How Do I Get Tested For Bacterial Vaginosis/BV?

Clue cells are vaginal epithelial cells that are covered in bacteria. They are one way of diagnosing bacterial vaginosis. Photo Courtesy of the Public Health Image Library; CDC/M. Rein

Most healthcare providers test for BV in one of two ways.

Gram Stain

For this test, a swab is taken from the vagina, stained, and examined under a microscope. The doctor is looking to see whether the healthy lactobacilli of the vagina have been replaced by the “bad” bacteria characteristic of BV.

Clinical Criteria

If a woman has three of the four following criteria, she is considered to have BV:

  • "Clue Cells" present in a sample of her vaginal fluid – these are cells covered with the organisms characteristic of BV, which can be seen under a microscope.
  • Vaginal pH of >4.5
  • Discharge with a fishy odor – either before or after the addition of 10% KOH. This is called the whiff test, and it works because the bacterial compounds that produce the fishy odor smell more strongly at higher pH. This is also why women with BV have a more noticeable odor after vaginal intercourse.

At-Home Tests

There are also at-home tests available that claim they can detect BV; however, existing tests aren't actually tests for BV. Instead, they test for elevated vaginal pH. While elevated vaginal pH can be caused by BV, it can also be caused by other infections -- such as trichomoniasis. A negative test from one of these kits is a pretty good sign that you don't have BV, but it's not definitive. As mentioned above, if you have the other three symptoms of BV, a doctor might still consider it worth treating.

Closing Thoughts

It's worth noting that many doctors question whether or not it is worth treating BV in women who are asymptomatic, although there's some evidence of benefit for pregnant women with visible changes in their vaginal flora, even if they don't have symptoms. For most other women, there isn't clear data as to whether treatment has long-term benefits for their health, particularly since so many BV infections recur on a regular basis.

Fun Fact: BV isn't caused by sperm. The reason that the odor associated with BV is more common after unprotected sex is that semen is at a higher pH than vaginal secretions. Therefore, the elevated pH makes the odor more noticeable -- just like adding the KOH that is used for the whiff test.

Sources

Brocklehurst P, Gordon A, Heatley E, Milan SJ. Antibiotics for treating bacterial vaginosis in pregnancy. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000262. doi: 10.1002/14651858.CD000262.pub4.

Honest H, Forbes CA, Durée KH, Norman G, Duffy SB, Tsourapas A, Roberts TE, Barton PM, Jowett SM, Hyde CJ, Khan KS. Screening to prevent spontaneous preterm birth: systematic reviews of accuracy and effectiveness literature with economic modelling. Health Technol Assess. 2009 Sep;13(43):1-627. doi: 10.3310/hta13430.

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