Amsel criteria
In clinical practice BV can be diagnosed using the Amsel criteria:
Thin, white, yellow, homogeneous discharge
Clue cells on microscopy
pH of vaginal fluid >4.5
Release of a fishy odor on adding alkali—10% potassium hydroxide (KOH) solution.At least three of the four criteria should be present for a confirmed diagnosis. A modification of the Amsel criteria accepts the presence of two instead of three factors and is considered equally diagnostic. Gram stain
An alternative is to use a Gram-stained vaginal smear, with the Hay/Ison criteria or the Nugent criteria. The Hay/Ison criteria are defined as follows:
Grade 1 (Normal): Lactobacillus morphotypes predominate. Grade 2 (Intermediate): Some lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present. Grade 3 (Bacterial Vaginosis): Predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent lactobacilli. (Hay et al., 1994)Gardnerella vaginalis is the main culprit in BV. Gardnerella vaginalis is a short, Gram-variable rod (coccobacillus). Hence, the presence of clue cells and gram variable coccobacilli are indicative or diagnostic of bacterial vaginosis. Nugent score
The Nugent score is now rarely used by physicians due to the time it takes to read the slides and requires the use of a trained microscopist. A score of 0-10 is generated from combining three other scores. The scores are as follows:
0–3 is considered negative for BV
4–6 is considered intermediate
7+ is considered indicative of BV.At least 10–20 high power (1000× oil immersion) fields are counted and an average determined. DNA hybridization testing with Affirm VPIII was compared to the Gram stain using the Nugent criteria.
This test, called the whiff test, is performed by adding a small amount of potassium hydroxide to a microscope slide containing the vaginal discharge. A characteristic fishy odor is considered a positive whiff test and is suggestive of bacterial vaginosis. Loss of acidity. To control bacterial growth, the vagina is normally slightly acidic with a pH of 3.8–4.2. A swab of the discharge is put onto litmus paper to check its acidity. A pH greater than 4.5 is considered alkaline and is suggestive of bacterial vaginosis. The presence of clue cells on wet mount. Similar to the whiff test, the test for clue cells is performed by placing a drop of sodium chloride solution on a slide containing vaginal discharge. If present, clue cells can be visualized under a microscope. They are so-named because they give a clue to the reason behind the discharge. These are epithelial cells that are coated with bacteria.Differential diagnosis for bacterial vaginosis includes the following:
Normal vaginal discharge. Candidiasis (thrush, or a yeast infection). Trichomoniasis, an infection caused by Trichomonas vaginalis. Aerobic vaginitisThe Center for Disease Control (CDC) defines STIs as "a variety of clinical syndromes and infections caused by pathogens that can be acquired and transmitted through sexual activity." But the CDC does not specifically identify BV as sexually transmitted infection.