GSABC JOURNAL OF BLOOD SERVICES Health care utilization of patients diagnosed with idiopathic thrombotic thrombocytopenic purpura in a commercially insured population in the United States Peter M. Wahl, Rhonda L. Bohn, Deirdra R. Terrell, James N. George, and Bruce Ewenstein BACKGROUND: Incident idiopathic thrombotic thromb- ocytopenic purpura (TTP) is an uncommon, potentially fatal blood disorder for which there are little or no data on health care costs. STUDY DESIGN AND METHODS: Patients satisfying a validated claims-based algorithm including an inpatient diagnosis of TTP and plasma exchange (PE) procedure during the period January 1, 2001 to May 31, 2008 were identified in the HealthCore Integrated Research Database. To characterize patterns of treatment and payments, a quantitative evaluation of comorbidities and treatments, health care utilization, and payments among this population of patients was conducted. All patients were followed until death, end of health plan enrollment, or 365 days after the TTP hospitalization, whichever occurred first. RESULTS: One hundred fifty-one patients met the claims coding algorithm. Mean total health care pay- ments for the TTP hospitalization were $56,347 (stan- dard deviation [SD] $80,230). Ten patients (6.6%) died during the hospitalization for TTP. Mean payments for PE services in the month following discharge were $9127 (SD $20,840). Several patients required pro- longed PE during the acute TTP phase (up to 116 separate exchanges over a period of 365 days), pro- longing required treatment and skewing payments and resource utilization during the 365-day period following discharge from the index TTP hospitalization. CONCLUSION: These data document the health care resource utilization by patients with idiopathic TTP, demonstrating that management of these patients is not only expensive but also skewed, with some patients requiring prolonged treatment. These data can contrib- ute to cost-effectiveness models when new treatments for TTP become available. INTRODUCTION I diopathic thrombotic thrombocytopenic purpura (TTP) is an uncommon, potentially fatal blood dis- order characterized by systemic microvascular thrombosis resulting in tissue ischemia and end- organ damage. 1 Idiopathic TTP, the subgroup of patients without associated disorders, has an incidence of approxi- mately 4.46 per million per year in the state of Oklahoma. 2 The annual incidence of patients with a severe deficiency of the plasma enzyme, ADAMTS13, a marker for the sub- group of patients who have an identified etiology for their TTP and therefore a more definitive diagnosis, was 1.74 per million in the state of Oklahoma. 2 Patients with severe ADAMTS13 deficiency are almost all within the subgroup of idiopathic TTP. These data from Oklahoma represent the only population-based estimates of the incidence of TTP. Before the discovery of effective treatment with plasma exchange (PE), survival was only 10%. 3 With the documentation that treatment with PE increased survival ABBREVIATIONS: DCI = Deyo-Charlson Comorbidity Index; HIRD = HealthCore Integrated Research Database; PE = plasma exchange; SSDMF = Social Security Death Master File; TTP = thrombotic thrombocytopenic purpura. From HealthCore, Inc., Wilmington, Delaware; Rhonda L. Bohn LLC, Waban, Massachusetts; Department of Biostatistics and Epidemiology, College of Public Health, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma; and Baxter Healthcare Corporation, Westlake Village, California. Address correspondence to: Peter M. Wahl, MLA, MS, Department of Medicine, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital, 1620 Tremont Street, Suite 3030, Boston, MA 02120; e-mail: pwahl@ hsph.harvard.edu. Support for this manuscript was provided by Baxter International. Received for publication December 19, 2011; revision received March 8, 2012, and accepted April 4, 2012. doi: 10.1111/j.1537-2995.2012.03758.x TRANSFUSION 2012;52:1614-1621. 1614 JBSM Volume 52, July 2012