The incidence of thrombotic thrombocytopenic purpura‐hemolytic uremic syndrome: all patients, idiopathic patients, and patients with severe ADAMTS‐13 deficiency

Background: Accurate estimates of the incidence of thrombotic thrombocytopenic purpura (TTP) are important to assess the resources required for current treatments as well as to anticipate the need to develop new treatments. Previous estimates have been indirect and have not reported data on patients with ADAMTS‐13 deficiency. Objective: To determine the incidence of patients with TTP‐hemolytic uremic syndrome (HUS) in three categories: all patients with clinically suspected TTP‐HUS, patients with idiopathic TTP‐HUS, and patients with severe ADAMTS‐13 deficiency. Methods: Incidence rates were estimated from the Oklahoma TTP‐HUS Registry, analyzing all 206 consecutive patients from January 1, 1996 to June 30, 2004 who were treated with plasma exchange for their initial episode of clinically suspected TTP‐HUS. ADAMTS‐13 activity was measured in 186 (90%) of the 206 patients. Results: The age–sex–race standardized annual incidence rates were 11.29 × 106 (95% CI: 9.70–12.88) for all patients with clinically suspected TTP‐HUS; 4.46 × 106 (95% CI: 3.43–5.50) for patients with idiopathic TTP‐HUS; and 1.74 × 106 (95% CI: 1.06–2.41) for patients with severe ADAMTS‐13 deficiency (