ADAMTS13 and thrombotic thrombocytopenic purpura: Adults with acquired idiopathic TTP require daily plasma exchange until neurologic symptoms have resolved and both a normal serum LDH and platelet count have been maintained for at least 2 to 3 days.43–46 Plasma exchange is thought to remove antibodies against ADAMTS13, while replacing the deficient protease.47,48 Plasma exchange results in the remission of TTP, which is usually fatal when untreated, in approximately 80%–90% of cases,49–52 generally without persistent organ damage.