What is KOH (Potassium Hydroxide)?
KOH is a 10% potassium hydroxide solution used as a diagnostic tool in clinical medicine to identify fungal infections and bacterial vaginosis by dissolving epithelial debris and allowing visualization of fungal elements or triggering the "whiff test" for vaginal infections. 1, 2
Primary Diagnostic Applications
Vaginal Infections
- KOH is applied to vaginal discharge specimens to diagnose candidiasis (yeast infections) and bacterial vaginosis 1
- The specimen should be collected via swab from the vaginal pool or walls and examined within 30 minutes to 2 hours for optimal results 1, 2
- For the "whiff test," a fishy amine odor released when KOH is added to vaginal discharge indicates bacterial vaginosis 1
- When examining for yeast, KOH dissolves cellular debris, making budding yeast and pseudohyphae easier to visualize under microscopy 1, 2
Dermatologic Fungal Infections
- KOH is the primary point-of-care test for identifying dermatophytes in skin, hair, and nail infections 2, 3
- For skin lesions, scrape the active border using a #15 scalpel blade or glass slide edge, then apply 1-2 drops of 10% KOH solution to the specimen on a glass slide 2
- The solution digests proteins, lipids, and epithelial debris, leaving fungal elements visible under microscopy 4, 5
Preparation Technique
Standard Method
- Place the specimen directly on a clean glass microscope slide 2
- Add 1-2 drops of 10% KOH solution 1
- Apply a coverslip and examine under microscopy 1, 2
- Begin examination under low power (10x) to scan, then switch to high-dry power (40x) for detailed visualization 2
Clinical Limitations and Pitfalls
Sensitivity Issues
- KOH preparation has only 40-80% sensitivity for detecting yeast compared to culture 1, 2
- Consider ordering culture when KOH is negative but clinical suspicion remains high, or in recurrent infections 1, 2
- For trichomoniasis, NAATs are strongly preferred over KOH wet mount due to superior sensitivity 2
Timing Constraints
- The specimen must be examined within 30 minutes to 2 hours of collection for vaginal specimens 1, 2
- Delayed examination reduces diagnostic accuracy, particularly for motile organisms like Trichomonas 1
Advantages in Clinical Practice
- KOH remains a simple, accurate, and inexpensive diagnostic technique providing immediate point-of-care results 2, 5
- The test enables rapid diagnosis without requiring expensive laboratory testing when combined with clinical findings 2
- Results are typically available within 1-2 hours of specimen collection 6