To determine the prevalence of immune thrombocytopenia (ITP) in Oklahoma regardless of age, clinical characteristics, insurance status, and source of health care. Patients with ITP were identified by the administrative code ICD-9-CM 287.3 in Oklahoma hematologists' offices for a 2-year period, 2003-2004. Prevalence was estimated separately for children (<16 years old) and adults because of their distinct clinical characteristics. Oklahoma census data for 2000 was used as the denominator. Eighty-seven (94%) of 93 eligible Oklahoma hematologists participated; 620 patients with ITP were identified. The average annual prevalences were as follows: 8.1 (95% CI: 6.7-9.5) per 100,000 children, 12.1 (95% CI: 11.1-13.0) per 100,000 adults, and 11.2 (95% CI: 10.4-12.0) per 100,000 population. Among children and adults less than age 70 years, the prevalence was greater among women. Among adults aged 70 years and older, the prevalence was greater among men. The highest prevalence of ITP was among men age 80 years and older. These data document for the first time the prevalence of ITP regardless of age, clinical characteristics, insurance status, and source of health care. The methodology developed for this prevalence analysis may be adaptable for epidemiologic studies of other uncommon disorders which lack specific diagnostic criteria and are treated primarily by medical specialists.
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