Well the results of the MEPEX trial would suggest otherwise. The trial was a randomized control trial in which 137 patients with ANCA-associated vasculitis and a serum Cr > 5.8mg/dL were randomized to receive either 7 sessions of plasma exchange over a 14 day period or Solu-Medrol 1000mg iv qd x 3d. In addition to these therapies, all patients also received prednisolone (1mg/kg/day, tapered over 6 months) + Cytoxan (2.5mg/kg/day x 3months) followed by Imuran for maintenance of remission.
Importantly, the plasma exchange arm was associated with an improved mortality and improved renal function (43 versus 19% risk of progression to ESRD at one year), and many of the patients in the pheresis arm were actually able to come off dialysis. The benefit was typically seen within the first 3 months of therapy, so many nephrologists will treat ANCA-associated vasculitis aggressively (e.g., pheresis, steroids, Cytoxan) for a good three months, and if they’re still on dialysis to stop if there’s no response.