Bacterial vaginosis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Laboratory Findings

Electrolyte and Biomarker Studies

To find out which of these is the case, a few simple tests are done. The healthcare provider will carry out a speculumexamination and take some swabs from high in the vagina. These swabs will be tested for:

• A characteristic smell—this is called the whiff test. A small amount of an alkali is added to a microscope slide that has been swabbed with the discharge—a 'fishy' odour is a positive result for bacterial vaginosis.
• Loss of acidity—the vagina is normally slightly acidic (with a pH of 3.8–4.2), which helps to control bacteria. A swab of the discharge is put onto litmus paper to check the acidity. A positive result for bacterial vaginosis would be a pH of over 4.5.
• 'Clue cells'—so called because they give a clue to the reason behind the discharge. These are epithelial cells (like skin) that are coated with bacteria. They can be seen under microscopic examination of the discharge.

Two positive results in addition to the discharge itself are enough to diagnose BV. If there is no discharge, then all 3 criteria are needed.

Amsel Criteria

In clinical practice bacterial vaginosis (BV) is diagnosed using the Amsel criteria:

1. Thin, white, yellow, homogeneous discharge
2. Clue cells on microscopy
3. pH of vaginal fluid >4.5
4. 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.

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): Mixed flora with 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)

What this technique loses in interobserver reliability, it makes up in ease and speed of use.

The standard for research are the Nugent Criteria. In this scale a score of 0-10 is generated from combining three other scores. It is time consuming and requires trained staff but is has high interobserver reliability:

• 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.

Lactobacillus morphotypes — average per high powered (1000× oil immersion) field. View multiple fields.	Gardnerella / Bacteroides morphotypes — average per high powered (1000× oil immersion) field. View multiple fields.	Curved Gram variable rods — average per high powered (1000× oil immersion) field. View multiple fields (note that this factor is less important — scores of only 0–2 are possible)
Score 0 for >30 Score 1 for 15–30 Score 2 for 14 Score 3 for <1 (this is an average, so results can be >0, yet <1) Score 4 for 0	Score 0 for 0 Score 1 for <1 (this is an average, so results can be >0, yet <1) Score 2 for 1–4 Score 3 for 5–30 Score 4 for >30	Score 0 for 0 Score 1 for <5 Score 2 for 5+

A recent study compared the gram stain using the Nugent criteria and the DNA hybridization test Affirm VPIII in diagnosing BV. The Affirm VPIII test detected Gardnerella in 107 (93.0%) of 115 vaginal specimens positive for BV diagnosed by gram stain. The Affirm VPIII test has a sensitivity of 87.7% and specificity of 96% and may be used for the rapid diagnosis of BV in symptomatic women.