Tests for Bacterial Vaginosis
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.
Why It Is Done
Tests for bacterial vaginosis are done to help find the cause of an abnormal vaginal discharge or other symptoms of a vaginal infection, such as vaginal irritation or pain.
How To Prepare
Do not douche, have sex, or use vaginal medicines for 24 hours before having a bacterial vaginosis test.
These tests are not usually done during your menstrual period.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?) .
How It Is Done
You will take off your clothes below the waist. You will have a gown to drape around your waist. You will then lie on your back on an examination table with your feet raised and supported by stirrups. This is similar to having a pelvic examination or Pap test.
Your doctor will put an instrument with curved blades (speculum) into your vagina. The speculum gently spreads apart the vaginal walls, allowing your doctor to see the inside of the vagina and the cervix. See a picture of the vaginal speculum examination.
Samples of fluid inside the vagina are then collected with a swab or wooden stick.
How It Feels
You may feel some discomfort when the speculum is put in, especially if your vagina is irritated and tender.
There is little or no risk in having a bacterial vaginosis test.
Tests for bacterial vaginosis take samples of fluid and cells from the vagina to see if this vaginal infection is present.
A high vaginal pH, clue cells, and a fishy odor usually are enough signs that bacterial vaginosis is present.
No abnormal vaginal discharge is present on vaginal exam.
A wet mount does not show large numbers of bacteria, such as Gardnerella, that cause bacterial vaginosis.
No clue cells are present.
No fishy odor is present when a potassium hydroxide (KOH) solution is added to a sample of vaginal discharge.
Vaginal pH is in the normal range of 3.8 to 4.5.
A bacterial vaginosis infection is present.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- If you are having your menstrual period.
- If you use a vaginal medicine, such as a nonprescription vaginal yeast medicine, 2 to 3 days before this test.
- Having sex or douching 24 hours before this test.
What To Think About
- Bacterial vaginosis during pregnancy increases a woman's risk of early (preterm) delivery. Because of this risk, it is important to treat bacterial vaginosis during pregnancy with antibiotics.
- Experts disagree about calling bacterial vaginosis a sexually transmitted disease (STD). A history of STDs or having multiple sex partners increases the chance of developing bacterial vaginosis. The actual number of bacterial vaginosis infections spread through sexual contact is not fully known.
- U.S. Preventive Services Task Force (2008). Screening for bacterial vaginosis in pregnancy to prevent preterm delivery: U.S. Preventive Services Task Force recommendation statement. Annals of Internal Medicine, 148(3): 214–220.
- Centers for Disease Control and Prevention (2006). Diseases characterized by vaginal discharge section of Sexually transmitted diseases treatment guidelines. MMWR, 55(RR-11): 49–56.
Other Works Consulted
- Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.
|Author||Sandy Jocoy, RN|
|Editor||Kathleen M. Ariss, MS|
|Associate Editor||Pat Truman, MATC|
|Primary Medical Reviewer||Sarah Anne Marshall, MD - Family Medicine|
|Specialist Medical Reviewer||Jeanne Marrazzo, MD, MPH - Infectious Disease|
|Last Updated||February 18, 2010|
Last Updated: February 18, 2010