ADAMTS13-related parameters at presentation in 32 surviving TMA patients. The level of ADAMTS13 activity in survivors at initial clinical remission defines 3 groups of TMA patients: below 5% (group 1, n = 13, black histograms), 15% to 40% (group 2, n = 12, dashed histograms), and 50% to 100% (group 3, n = 7, white histograms). At presentation, the percentage of patients with either a decreased ADAMTS13Ag level, an ADAMTS13 inhibitor (independently of the titer), or the presence of an anti-ADAMTS13 IgG, IgM, or IgA was not significantly different between the 3 groups. In contrast, at presentation, the presence of either a high titer of ADAMTS13 inhibitor or a highly inhibitory anti-ADAMTS13 IgG was significantly (*P < .05) more frequent in group 1 when compared with group 2 and group 3, respectively.