PEX complications have been documented as described previously16 in all Registry patients from June 25, 1996 through June 24, 2011. Results have been analyzed every 3 years. The data describe the results of the 5 consecutive 3-year periods for 66 patients with ADAMTS13 activity < 10%. Of the 70 patients described in Table 3, 1 patient died before a central venous catheter was placed for PEX, 2 patients presented before June 25, 1996, and 1 patient presented after June 24, 2011. A 1-sided Cochran-Armitage Trend test was performed to determine whether the proportion of patients with major complications, days of PEX, or treatment with steroids or rituximab changed across the 5 time periods. Adapted with permission from Som et al.5