What is KOH (Potassium Hydroxide)?

Potassium Hydroxide (KOH): Clinical Applications in Diagnostic Medicine

KOH is a strong alkali solution primarily used in clinical practice as a diagnostic tool to identify fungal elements, assess for bacterial vaginosis, and occasionally as a treatment for certain skin conditions.

Diagnostic Applications

Vaginal Infections

KOH plays a crucial role in diagnosing common vaginal conditions:

• 10% KOH preparation is used for microscopic examination of vaginal discharge 1
• KOH whiff test: Adding 10% KOH to vaginal discharge produces an amine or "fishy" odor when positive, suggesting bacterial vaginosis (BV) 1
• Fungal identification: KOH dissolves epithelial cells while preserving fungal elements, making yeast or pseudohyphae of Candida species more easily visible under microscope 1

Diagnostic Protocol for Vaginal Infections

1. Collect vaginal discharge specimen
2. Place sample on two slides:
   • One with 1-2 drops of 0.9% normal saline
   • One with 10% KOH solution
3. Apply cover slips and examine under microscope:
   • Saline slide: Look for motile T. vaginalis or clue cells (BV)
   • KOH slide: Look for yeast or pseudohyphae of Candida species 1

Diagnostic Criteria for Bacterial Vaginosis

Clinical diagnosis requires three of the following:

• Homogeneous, white discharge coating vaginal walls
• Presence of clue cells on microscopic examination
• Vaginal pH > 4.5
• Positive whiff test (fishy odor after adding 10% KOH) 1

Test Characteristics

• Sensitivity: KOH preparation sensitivity ranges from 40-80% depending on specimen quality and examiner expertise 2
• Transport time: Specimens for KOH examination should be submitted in 0.5 mL saline or transport swab and examined within 2 hours at room temperature 1
• Advantages: Simple, rapid, inexpensive point-of-care test
• Limitations: Examiner dependent, moderate sensitivity compared to culture or molecular methods 2

Therapeutic Applications

Though primarily diagnostic, KOH has therapeutic applications:

• Molluscum contagiosum: 10% KOH solution applied topically has shown 92.5% clearance rate in children after approximately 4 weeks of treatment 3, 4
• Mechanism: KOH digests proteins, lipids, and epithelial debris 5
• Side effects: Local irritation, stinging, and occasionally hypopigmentation 3

Clinical Pearls

• When KOH is positive but PCR negative, the test should be considered presumptively positive, and appropriate treatment should be initiated based on clinical presentation 2
• KOH may detect non-viable fungal elements that PCR cannot detect 2
• The technique of KOH preparation is increasingly becoming a "disappearing clinical art form" despite its utility 6
• For optimal results, specimens should be examined promptly (within 2 hours) 1

Pitfalls to Avoid

• Inadequate specimen collection can lead to false-negative results
• Delayed examination (>2 hours) may reduce sensitivity
• Overreliance on KOH alone without considering clinical context
• Failure to properly prepare the specimen (inadequate mixing with KOH solution)
• Not allowing sufficient time for KOH to dissolve epithelial cells before microscopic examination

KOH preparation remains a valuable, cost-effective diagnostic tool that provides rapid results at the point of care when properly performed and interpreted.