Determination of ADAMTS13 activity by immunoblotting of VWF substrate degraded by BaCl₂-activated ADAMTS13 in patient plasma (diluted 1:20). Lanes 1-7: assay calibration by normal plasma dilutions of 1:20 (100% activity), 1:40 (50%), 1:80 (25%), 1:160 (12.5%), 1:320 (6.25%), 1:640 (3%), and buffer control (0%). Sister 1: acute initial TTP episode (lane 8); clinical remission 17, 35, and 37 months after the initial episode (lanes 9-11). Sister 2: acute initial TTP episode (lane 12); clinical remission 5, 23, and 25 months after the initial episode (lanes 13-15).