MPO and vasculitis: On the basis of our results reported here and the data about MPO-ANCA and relapse risk derived from other studies, paired with what we now know about variable efficacy of rituximab versus azathioprine (and by proxy, MMF and methotrexate), we propose an algorithm that utilizes the serial determination of the MPO-ANCA status after remission induction to guide the institution of effective remission-maintenance treatment in patients with MPO-ANCA–associated vasculitis with GN (Figure 3).