The utility of patient characteristics in predicting severe ADAMTS13 deficiency and response to plasma exchange.

Background: Idiopathic thrombotic thrombocytopenic purpura (TTP) is a rare form of thrombotic microangiopathy (TMA) characterized by extreme deficiency of ADAMTS13, an enzyme responsible for cleavage of von Willebrand factor. Plasma exchange therapy is the cornerstone of current treatment and is ineffective for most other forms of TMA. The availability of ADAMTS13 testing has improved diagnostic accuracy and appropriate selection of patients who are most likely to respond to plasma exchange.