title: Prevalence of immune thrombocytopenia: analyses of administrative data.
abstract: BACKGROUND
  The prevalence of immune thrombocytopenic purpura (ITP) in the USA is unknown. The paucity of data makes clinical trial design and resource allocation challenging.
  
  
  OBJECTIVE
  We aimed to quantify the prevalence of ITP in one state and to report on utilization of resources.
  
  
  METHODS
  The Maryland Health Care Commission supplied utilization data on all privately insured Maryland residents in 2002. We identified patients having two claims, separated by at least 30 days, for International Classification of Diseases, Ninth Revision, Clinical Modification code 287.3 (expected to be predominantly ITP). We excluded patients with concurrent diagnoses that made ITP unlikely. In sensitivity analyses, we varied the required visit interval between 14 and 180 days. We quantified ITP prevalence, resource utilization, and prevalence of concurrent autoimmune illnesses.
  
  
  RESULTS
  The age-adjusted prevalence of ITP was 9.5 per 100,000 persons (10.5 per 100,000 when requiring a minimum 14-day interval and 4.5 per 100,000 with a 180-day interval). There was a predominance of males in childhood and of females in the middle-adult years, with an overall prevalence rate ratio of 1.9 for females to males. Twenty per cent of these patients were hospitalized, but emergency department use was rare, as was splenectomy. A concurrent diagnosis of multiple sclerosis was 25 times more prevalent than anticipated.
  
  
  CONCLUSIONS
  We conclude that the prevalence of ITP in one populous state in the USA is comparable with that which has been reported in Europe. The suggested co-occurrence of ITP and multiple sclerosis in children merits further investigation.
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. jsegal@jhmi.edu
authors.forename: J B
authors.initials: JB
authors.lastname: Segal
authors.forename: N R
authors.initials: NR
authors.lastname: Powe
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D005060:Europe; D005260:Female; D006801:Humans; D007223:Infant; D038801:International Classification of Diseases; D008297:Male; D008396:Maryland; D008499:Medical Records; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications / Q000453:epidemiology; D015995:Prevalence; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000150:complications / Q000453:epidemiology* / Q000628:therapy; D012737:Sex Factors