MPO and microscopic polyangiitis: A pooled analysis from two large RCTs, RAVE and WGENT, found in 2016 that the risk of exacerbations in the MPO-ANCA-positive GPA and PR3-positive GPA groups did not differ from each other, but in the former group, it was higher than in the MPO-positive MPA group at both 12 and 18 months of follow-up.