ADAMTS13 and anti-ADAMTS13 antibodies as markers for recurrence of acquired thrombotic thrombocytopenic purpura during remission

Background : from 20 to 50% of patients who survive an acute episode of the acquired form of thrombotic thrombocytopenic purpura relapse but clinical and laboratory markers of recurrence are not well established Design and methods : in 109 patients enrolled in an international registry we evaluated, in the frame of a retrospective cohort study, the predictive role of the metalloprotease ADAMTS13 as measured in plasma during remission. Anti-ADAMTS13 antibodies and von Willebrand factor were also evaluated in a smaller number of the same patients Results : median values of ADAMTS13 activity and antigen were significantly lower in patients with recurrent thrombotic thrombocytopenic purpura than in those with no recurrence (activity: 12% vs. 41%; p=0.007; antigen: 36% vs. 58%; p=0.003). A severe deficiency of ADAMTS13 activity (10% or less) was associated with a higher likelihood of recurrence (odds ratio 2.9; 95% confidence interval 1.3 to 6.8; p=0.01). Anti-ADAMTS13 antibodies were also more prevalent in patients with recurrent thrombotic thrombocytopenic purpura (odds ratio 3.1; 95% confidence interval 1.4 to 7.3; p=0.006). The presence during remission of both severe ADAMTS13 deficiency and anti-ADAMTS13 antibodies increased the likelihood of recurrence 3.6 times (95% confidence interval 1.4 to 9.0; p=0.006). The presence of ultralarge von Willebrand factor multimers and of associated diseases or conditions did not increase recurrence Conclusions : survivors of an acute episode of acquired thrombotic thrombocytopenic purpura with severely reduced levels of ADAMTS13 and/or with anti-ADAMTS13 antibodies during remission have an approximately three-fold greater likelihood of developing another episode of thrombotic thrombocytopenic purpura than patients with higher protease activity and no antibody