A 14-year-old girl has had nausea, intermittent diarrhea, and a 2.2-kg (5-lb) weight loss over the past 4 weeks. Examination shows a migrating serpiginous pruritic perianal rash. Her leukocyte count is 8000/mm³ with0% eosinophils. Which of the following tests is most likely to yield an accurate diagnosis?
A) Stool examination for ova and parasites
B) Serum antineutrophil cytoplasmic antibody (ANCA) levels
C) Skin biopsy
D) Thyroid function tests