PRTN3 and microscopic polyangiitis: 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