title: New-onset and idiopathic thrombotic thrombocytopenic purpura: incidence, diagnostic validity, and potential risk factors.
abstract: OBJECTIVE
  The aim of this study was to determine the incidence rate for new-onset and idiopathic thrombotic thrombocytopenic purpura (TTP) among adults 20-64 years old, the validity of diagnostic criteria, and potential risk factors for TTP.
  
  
  METHODS
  This retrospective observational study analyzed automated administrative data from 11 geographically dispersed U.S. health plans. Cases of TTP were identified based on the presence of an inpatient hospital claim for TTP (ICD-9-CM 446.6) between 1/1/97 and 12/31/01 and confirmed by medical record review. Pharmacy and medical claims were used to evaluate outpatient drug exposure and comorbidities preceding hospitalization for TTP. Cases and the base population were screened so as to result in an incidence rate for idiopathic TTP.
  
  
  RESULTS
  We confirmed new-onset and idiopathic TTP in 9 of 15 presumptive cases for an incidence density of 1.4 per million person-years (95% CI: 0.6-2.6). The rate increased to 1.8 per million person-years after projection and age-standardization. The highest incidence rate of TTP was found in patients 50-64 years old (2.8 per million person-years; 95% CI: 0.8-7.1). These 9 patients had no apparent risk factors for TTP based on claims and medical record data.
  
  
  CONCLUSIONS
  In a general U.S. population, the incidence rate of confirmed new-onset and idiopathic TTP was lower than previously reported, but appears to be on the rise. Our findings suggest that administrative claims data are useful for identifying outpatient drug exposures and comorbidities potentially associated with TTP.
authors.affiliation: Center for Health Care Policy and Evaluation, Eden Prairie, MN 55344, USA. stephanie_d_schech@uhc.com
authors.forename: Stephanie D
authors.initials: SD
authors.lastname: Schech
authors.forename: Allen
authors.initials: A
authors.lastname: Brinker
authors.forename: Deborah
authors.initials: D
authors.lastname: Shatin
authors.forename: Margaret
authors.initials: M
authors.lastname: Burgess
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology; D012189:Retrospective Studies; D012307:Risk Factors