Q73
Single choice
An 18-year-old female presents for follow-up of a rash. She states that she has been using OTC antifungal preparations without success. She used OTC cortisone cream with mild improvement, but the lesions never disappeared. Her condition also recurred with full severity once the cortisone cream was discontinued. Her family history reveals a first degree relative with similar rash. The rash is over the elbows, trunk, and scalp .
Which of the following tests is most likely to confirm your clinical suspicion?