In acute pregnancy-onset TTP, ADAMTS13 may adopt several profiles of conformation. (A) ADAMTS13 antigen levels (3H9-ELISA) in iTTP (n = 52), uTTP (n = 27), and cTTP (n = 29). ADAMTS13 antigen was decreased (lower than the normal range) in all 108 patients. Median ADAMTS13 antigen level was 0.116 μg/mL (IQR, 0.133 μg/mL) in the iTTP group, 0.172 μg/mL (IQR, 0.148 μg/mL) in the uTTP group, and 0.052 μg/mL (IQR, 0.108 μg/mL) in the cTTP group as previously reported by Joly et al.38 Only plasma samples containing ADAMTS13 antigen of ≥0.03 μg/mL could be tested for ADAMTS13 conformation. (B) ADAMTS13 conformation (1C4-ELISA) in iTTP (n = 46), uTTP (n = 26), and cTTP (n = 11). The activating murine monoclonal antibody 17G2 was used as a positive control in all samples tested. ADAMTS13 conformation was found open in all but 1 patient with iTTP tested (45 of 46, 97.8%) and open in the majority of patients with uTTP tested (20 of 26, 76.9%). As previously reported by Joly et al, ADAMTS13 conformation was closed in all but 1 patient with cTTP.
