How is Microscopic polyangiitis diagnosed
The diagnosis is made on the basis of a characteristic clinical presentation and a renal biopsy showing necrotizing GN without immune deposits. A p-ANCA directed against MPO is found in up to 60% of patients and is supportive of the diagnosis. Notably, some patients (15%–30%) may have c-ANCA (directed against serine PR3), but MPA patients are less likely to have upper respiratory tract involvement (i.e., sinusitis), cavitary lung lesions, and/or granuloma formation on histology, separating it from GPA.
