Low ADAMTS13 Activity in Clinical Remission Predicts the Risk of TTP Relapses.

Idiopathic thrombotic thrombocytopenic purpura (TTP) is a devastating disorder characterized by frequent recurrences. A predictive biomarker that allows for the early identification and intervention prior to the overt relapse of disease is needed. In the present study, the assay for ADAMTS13 activity was modified to adequately detect ADAMTS13 activity as low as 0.5%. Serial samples (n=157) collected from 24 TTP patients during periods of sustained clinical remission were then studied. These patients were followed up quarterly for an average of 23 months, during which time 9 episodes of TTP relapses from 6 patients occurred. We measured ADAMTS13 activity in these samples and then employed logistic regression modeling to evaluate the relationship between ADAMTS13 activity levels and the risk of TTP relapses. Our data demonstrated that lower ADAMTS13 activity and younger age are significantly associated with a higher probability of relapse in the 3 months following the date the specimens were taken. In contrast, ADAMTS13 antibody IgG levels are not predictive of TTP relapses. Identification of low ADAMTS13 activity during remission as a key risk factor for TTP relapses provides a new screening strategy to identify patients who may benefit from prophylactic therapy prior to disease relapses.