Exams and Tests

Your doctor may only test you for bacterial vaginosis if you:

• Have symptoms.
• Are going to have a hysterectomy or surgical abortion (bacterial vaginosis increases infection risk afterwards).
• Are pregnant and have had a preterm delivery in the past (a past preterm delivery may have been caused by infection).

Your doctor can diagnose bacterial vaginosis based on your history of symptoms, a vaginal examination, and a sample of the vaginal discharge. Laboratory tests to detect signs of bacterial vaginosis may include:

• Wet mount. A sample of vaginal discharge is mixed with a salt (normal saline) solution after placing it on a microscope slide. The prepared slide is examined to identify the bacteria present, to look for white blood cells that indicate an infection, and to look for unusual cells called clue cells. The presence of clue cells is the most reliable indicator of bacterial vaginosis.
• Whiff test. Several drops of a potassium hydroxide (KOH) solution are added to a sample of vaginal discharge to determine whether a strong fishy odor is produced. A fishy odor on the whiff test suggests bacterial vaginosis.
• Vaginal pH. The normal vaginal pH is 3.8 to 4.5. Bacterial vaginosis usually causes the vaginal pH to rise above 4.5.
• Gram stain. A sample of the vaginal discharge is placed on a microscope slide. A special dye is applied to the slide, causing certain types of bacteria (Gram-positive bacteria) to turn a shade of purple while coloring others (Gram-negative bacteria) pink. In bacterial vaginosis, Gram-negative bacteria, especially Gardnerella vaginalis, are most common.
• Oligonucleotide probes. This test detects the genetic material (DNA) of bacterial vaginosis bacteria. Oligonucleotide probe testing is very accurate but is not routinely available in most labs.

The presence of clue cells, an increased vaginal pH, and a positive whiff test are enough evidence to treat for bacterial vaginosis.

Bacterial vaginosis may be detected during routine Pap testing. But Pap testing is not a standard test to diagnose bacterial vaginosis.