Time course of ADAMTS13 plasma activity in 3 patients for whom sequential measurements of ADAMTS13 plasma activity over several years are available. ADAMTS13 activity was measured during (1) a disease relapse before (^*) and during plasma exchange (⋄) or infusions of fresh-frozen plasma (‡) and (2) remission (#). R indicates relapse; RTX, rituximab; S, splenectomy; and Ab, antibody. Anti-ADAMTS13 antibodies were detected using the ELISA test. Sequential measurements of CD19⁺ cells are not available for patient 9. The length of the solid bars indicates the duration of TTP relapse.