Clinical response in patients with nonidiopathic and normal or mildly reduced ADAMTS13 activity. Six patients in this category were serially studied. All patients had plasma ADAMTS13 activity higher than 25% and no ADAMTS13 inhibitor on admission. Patients 21, 24, and 25 had hematopoietic stem cell transplantation–associated TTP. Patient 29 had idiopathic pulmonary sclerosis on FK506. Patients 31 and 33 had cancer- and clopidogrel-associated TTP, respectively. Patient 33 received 3 doses of vincristine (V) treatment prior to the study. All patients (except patient 24) died despite temporary recovery of platelet count in some patients (patients 29 and 31). The data shown are from the initial hospitalization. The ADAMTS13 activity shown in the figure was the mean of 2 independent analyses. PEx indicates plasma exchange; P, prednisone; and S, splenectomy.