Bacterial Vaginosis Diagnosis Using Wet Prep and Symptoms

Diagnostic Approach

The Centers for Disease Control and Prevention recommends using the Amsel criteria, which requires three of four findings: homogeneous white discharge, pH >4.5, positive whiff test, and clue cells on microscopy, for diagnosing bacterial vaginosis 1, 2, 3
The Amsel criteria include homogeneous, white, noninflammatory discharge that smoothly coats the vaginal walls 2
Clue cells, which are bacterial-covered epithelial cells, are visible on wet mount saline preparation 4, 5
Vaginal pH >4.5 is measured with narrow-range pH paper 4, 5
A positive whiff test, characterized by a fishy amine odor when vaginal secretions are mixed with 10% KOH, is also part of the Amsel criteria 4, 5, 1

The wet mount preparation involves collecting vaginal secretions with a cotton swab and placing them in 1 mL normal saline, then examining under microscope at low- and high-dry power for clue cells 4, 5
Clue cells are usually easily identified in the saline specimen 1, 3
Adding 10% KOH to a second slide produces the characteristic fishy odor if bacterial vaginosis is present 4, 5

The American College of Obstetricians and Gynecologists notes that while Gram stain is considered the gold standard laboratory method, it is not required for clinical diagnosis 7, 2
Gram stain determines the relative concentration of bacterial morphotypes but is more specific than necessary for routine clinical diagnosis 7
Culture of G. vaginalis is not recommended as a diagnostic tool because it lacks specificity—G. vaginalis can be isolated from half of normal women 1, 3
DNA probe tests and commercial card tests are available but not required when Amsel criteria can be applied 2

For symptomatic women, wet prep combined with pH and whiff test (Amsel criteria) provides adequate diagnostic accuracy for bacterial vaginosis without requiring Gram stain or culture 1, 2, 3
The key is identifying clue cells on wet mount microscopy along with two other Amsel criteria 4, 5