MSFinals-2904

A 50-year-old man visits his doctor with symptoms of a vasculitic rash, joint pains, and swollen ankles. He reports feeling unwell, fatigued, and experiencing weight loss. During the visit, his urine dipstick shows blood and protein, and urgent blood tests reveal worsening kidney function with elevated inflammatory markers. The doctor suspects microscopic polyangiitis and requests an autoimmune screening. What autoantibody is expected to be positive in this case?