Investigations for microscopic polyangiitis

Investigations commonly performed for most systemic vasculitides (including microscopic polyangiitis) are outlined in Investigations for systemic vasculitides. Investigations that may support a specific diagnosis of microscopic polyangiitis include:

• positive antineutrophil cytoplasmic antibody (ANCA)—seen in nearly all patients; if ANCA titres are persistent despite treatment, it can be indicative of poor prognosis
• impaired kidney function and nephritic urinary sediment (including red cells and red cell casts)
• characteristic changes on kidney biopsy—usually required to confirm the diagnosis.