ADAMTS13 antigen levels, ADAMTS13 conformation, and anti-ADAMTS13 autoantibody levels in iTTP patient samples during acute and remission phase. (A) Flow chart of patient inclusion. iTTP plasma samples (n = 209) from 140 iTTP patients were grouped into 4 categories according to their ADAMTS13 activity and disease state: acute iTTP (ADAMTS13 activity <10%, n = 41), iTTP in remission with ADAMTS13 activity <10% (n = 45), iTTP in remission with ADAMTS13 activity between 10% and 50% (n = 32), and iTTP in remission with ADAMTS13 activity >50% (n = 91). (B) ADAMTS13 antigen levels in plasma from acute iTTP patients (n = 41) and iTTP patients in remission (n = 140).⁵  Only samples containing ≥0.03 µg/mL (dotted line) could be tested for ADAMTS13 conformation. (C) ADAMTS13 conformation was tested in plasma samples from acute iTTP patients (n = 31), iTTP patients in remission with ADAMTS13 activity <10% (n = 43), iTTP patients in remission with ADAMTS13 activity between 10% and 50% (n = 32), and iTTP patients in remission with ADAMTS13 activity >50% (n = 91), using 1C4-ELISA. Filled circles, closed ADAMTS13; open circles, open ADAMTS13. (D) Anti-ADAMTS13 autoantibody levels (TTP07-A equivalents) in plasma from the patients in C were measured using ELISA. Filled circles, closed ADAMTS13; open circles, open ADAMTS13. Abs, antibodies.