Microbiology Test

Test : KOH preparation


Indications : The test is usually ordered if a person is suspected to have fungal infection of the skin. Symptoms which prompt the test include -

• Red, itchy or scaly skin
• Skin patches with blisters along the edges

The test is done on an outpatient basis. No preparation is required prior to the test.

A skin sample is taken by lightly scraping the affected area using a scalpel or the edge of a microslide. Care must be taken to avoid bleeding while scraping. If hair sample is required, a forcep is used to remove the hair shaft and follicles from the infected area. The sample is then placed on a slide and is treated with KOH solution and DMSO, a solvent, which can slowly but effectively dissolve the skin cells but not the fungus. This is allowed to stand for fifteen minutes. The intact fungal cells may be stained (if necessary) with lactophenol cotton blue stain and viewed using a microscope.

Physiology : The KOH (potassium hydroxide) preparation is a quick and inexpensive test that is carried out to detect fungal infections of the skin, nails or hair. It also helps to differentiate between the fungal infections like Candida albicans and dermatophyte infections from other skin ailments such as psoriasis and eczema.

Normal Range : No fungus elements identified

Interpretation : Normal
Fungal cells absent in the skin samples.

Abnormal
Fungal cells present in the skin, hair or nail samples indicates fungal infection. This may indicate ringworm, jock itch, athlete’s foot or any other fungal infection.

If fungal infection is ruled out and if the skin patches persist then other tests must be carried out to find out the underlying reason.

Sample : Fungal specimen

Test Method : 10% KOH with gentle heat, alternately 20% KOH or 10% KOH and 40 % dimethyl sulfoxide (DMSO)

Related Tests : Fungus smear, Gram stain, Indian ink preparation.

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