ADAMTS13 and thrombotic thrombocytopenic purpura: Mildly or moderately decreased ADAMTS13 activity (18–48% of normal in 4 of the 22 patients, the other 18 displaying normal activity >50%) (Table 4) as well as normal [50] or subnormal to normal levels [30,45,49] in several previously described patients clearly ruled out thrombotic thrombocytopenic purpura (TTP), which is characterized by <10% (and indeed often <1%) ADAMTS13 activity [51].