Previous studies have shown that the specificity of IIF for ANCA testing is close to 93%, whereas sensitivity is approximately 67% to 78%, and additional tests are needed to improve this performance.4 ELISA can play this role.4 In this case, proteins with individual antigen specificities are used − particularly PR-3 and MPO.1 The specific determination of anti-PR3 and anti-MPO antibodies is useful in differential diagnosis of systemic vasculites, particularly when differentiating between GPA, MPA and EGPA, which have diverse clinical presentations, prognoses and treatment responses.10 The gene discussed is PRTN3; the disease is granulomatosis with polyangiitis.