KOHnäyte

KOHnäte, in clinical microscopy often referred to as KOH mounts, are microscopic preparations used to detect fungal elements in patient samples. They are prepared by suspending or placing a small amount of material from skin, hair, or nails in a potassium hydroxide solution on a glass slide. The KOH clears keratin and other tissues, making fungal structures such as hyphae, pseudohyphae, or yeast cells more readily visible under standard light microscopy.

Preparation and interpretation

Typical samples include skin scrapings, hair, or nail clippings. After applying 10–20% potassium hydroxide and gently warming, the specimen is covered with a cover slip and examined within minutes to hours. In some settings, optional stains (such as methylene blue or calcofluor white for fluorescence) may be used to enhance visualization. A positive KOH mount shows fungal elements consistent with dermatophytes or yeasts; a negative result does not completely rule out infection, as organisms may be sparse or unevenly distributed.

Advantages and limitations

KOHnäte are inexpensive, rapid, and can be performed at the point of care without specialized equipment. They provide immediate provisional information to guide treatment. Limitations include variable sensitivity and specificity, dependence on the examiner’s experience, and the inability to determine the exact fungal species. If clinical suspicion remains high or if species identification is required, culture or molecular methods may be employed as follow-up.

Safety and handling

Potassium hydroxide is caustic; appropriate safety measures are required, including gloves and eye protection, and proper disposal of used slides.

See also: KOH test, fungal microscopy, dermatology, mycology.