Tests for Bacterial Vaginosis

Bacterial Vaginosis Tests

Test Overview

Tests for bacterial vaginosis take samples of fluid and cells from the vagina to see if this vaginal infection is present. Bacterial vaginosis has also been called nonspecific vaginitis, Haemophilus vaginitis, or Gardnerella vaginitis.

Bacterial vaginosis is caused by a change in the balance of microorganisms found in a healthy vagina. A healthy vagina normally has many microorganisms in it. The microorganisms involved in bacterial vaginosis include Gardnerella, Mobiluncus, Bacteroides, and Mycoplasma. When bacterial vaginosis is present, these microorganisms increase in number while the number of healthy microorganisms decrease.

Many women with bacterial vaginosis do not have symptoms. The most common symptom of bacterial vaginosis is an increase in a grayish white vaginal discharge, unlike normal vaginal discharge. The discharge often has a fishy smell.

Women who have bacterial vaginosis during pregnancy have a higher chance of miscarriage, early (preterm) delivery, and an infection after delivery, so it is important for pregnant women who have symptoms to be tested for bacterial vaginosis.

The U.S. Preventive Services Task Force (USPSTF) says that studies do not show support for or against testing pregnant women at high risk for preterm delivery who do not have symptoms for bacterial vaginosis.¹ The U.S. Centers for Disease Control and Prevention (CDC) supports—but has no firm guidelines for—screening pregnant women without symptoms who have had a preterm delivery in the past.²

Several tests can be used to find bacterial vaginosis:

• Wet mount. A sample of vaginal discharge is mixed with a salt solution on a microscope slide. The slide is checked for bacteria, white blood cells, and unusual cells called clue cells. If clue cells are present, it means bacterial vaginosis is present.
• Whiff test. Several drops of a potassium hydroxide (KOH) solution are added to a sample of vaginal discharge to see whether a strong fishy odor is produced. A fishy odor on the whiff test usually means bacterial vaginosis is present.
• Vaginal pH. The normal vaginal pH is 3.8 to 4.5. Bacterial vaginosis often causes the vaginal pH to be greater than 4.5.
• Gram stain. A sample of the vaginal discharge is placed on a microscope slide. A special dye is put on the slide. This causes certain types of bacteria (Gram-positive bacteria) to turn a shade of purple while others (Gram-negative bacteria) turn pink. In bacterial vaginosis, it is most common to have Gram-negative bacteria, especially Gardnerella.
• Oligonucleotide probes. This test finds the genetic material (DNA) of this bacteria. An oligonucleotide probe test is very accurate but is not available in all labs.

Bacterial vaginosis may be found during a Pap test. But a Pap test is not recommended as a test to find bacterial vaginosis.

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Author:	Sandy Jocoy, RN	Last Updated: February 18, 2010
Medical Review:	Sarah Anne Marshall, MD - Family Medicine Jeanne Marrazzo, MD, MPH - Infectious Disease
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