KOH whiff test
Summary
The whiff test adds 10% potassium hydroxide to vaginal discharge and is positive when a fishy amine odour is released. A positive whiff test is one of the Amsel criteria for bacterial vaginosis.
Detail
KOH alkalinizes the specimen, volatilizing the amines (cadaverine, putrescine, trimethylamine) produced by the anaerobic overgrowth of bacterial vaginosis, chiefly Gardnerella vaginalis with Prevotella, Mobiluncus, and Atopobium. Diagnosis by Amsel criteria requires three of four: thin homogeneous grey-white discharge, vaginal pH above 4.5, positive whiff test, and clue cells (squamous epithelial cells studded with adherent coccobacilli obscuring their borders) on saline wet mount. Bacterial vaginosis represents loss of the normal lactobacilli that keep vaginal pH acidic; it is not classically an inflammatory condition, so there are few white cells, and it is not considered a sexually transmitted infection although it is associated with sexual activity. It increases risk of preterm labour, PID, and acquisition of other STIs, and is treated with metronidazole or clindamycin. KOH preparation is used separately in dermatology and for candidiasis, where it dissolves keratin to reveal pseudohyphae and budding yeast; in candidal vaginitis the discharge is thick and white, pH is normal, and the whiff test is negative.
Sources
- Levinson Medical Microbiology and Immunology
- First Aid for the USMLE Step 1
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