A 23 year-old African American female presents with "lightening" of the skin in various areas. To confirm her diagnosis of vitiligo, which test is indicated?

To confirm a diagnosis of vitiligo, a skin biopsy is often utilized. This test allows for the examination of the skin at a microscopic level, which can help distinguish vitiligo from other skin conditions that may cause depigmentation. In vitiligo, the biopsy typically shows the absence or reduction of melanocytes within the epidermis. This finding is pivotal in establishing the diagnosis when clinical features alone may not provide sufficient clarity.

A Wood's light examination can aid in assessing changes in skin pigmentation as it enhances the contrast between normal and depigmented skin by causing the affected areas to appear lighter; however, it does not provide definitive evidence for vitiligo. A KOH prep is primarily used to identify fungal infections, such as tinea, and would not assist in diagnosing vitiligo. Similarly, a Gram stain is used for identifying bacterial infections and is not applicable to the evaluation of skin conditions like vitiligo. Thus, the skin biopsy stands out as the most appropriate method for confirming a diagnosis of vitiligo.