To confirm tinea infections such as tinea barbae, which diagnostic test is commonly used?

• A. Gram stain
• B. Wood's lamp examination
• C. KOH prep
• D. Skin culture

Answer: (C)

Direct visualization of fungal elements in skin scrapings is the key approach for confirming dermatophyte infections like tinea barbae. A potassium hydroxide preparation clears keratin from the sample, so fungal hyphae or yeast forms become visible under light microscopy. This method is rapid, inexpensive, and typically performed in the clinic, providing immediate confirmation when dermatophyte structures are seen.

Other tests have limitations: Wood's lamp relies on fluorescence, which varies by organism and is often negative in beard-area infections, so it isn’t consistently reliable for confirmation. Gram stain can show inflammatory changes but isn’t specific for fungi and may miss fungal elements. Skin cultures are more definitive and can identify the exact organism and guide therapy, but they take days to weeks, making them less practical for immediate confirmation.