Prevalence Estimates of Adult Chronic Idiopathic Thrombocytopenic Purpura (ITP) in the United States.

ITP is a disease caused by inadequate platelet production as well as increased platelet destruction. Literature on the epidemiology of ITP is currently sparse and the disease remains poorly described. Based on previous reviews, the overall incidence of ITP among adults ranges from 1.6 to 3.0 per 100,000 person years of observation (PYO); prevalence estimates range from 2.1 to approximately 36.4 per 100,000 persons (Neylon AJ et al., Br J Haematol. 2003; Satia J et al., Eur Hematol Assoc. [poster presentation] 2006; Deitz AC et al., Blood. 2006). In this study, the objective was to estimate the prevalence of adult chronic ITP (in 2005) stratified by age and gender using a large US claims database (Integrated Healthcare Information Services, IHCIS). IHCIS comprises over 70 million patients from 45 health plans. Adult chronic ITP cases were defined as patients with at least two diagnoses (ICD-9 code 287.3) for primary thrombocytopenia separated by at least 6 months between 2002 and 2006, and age 18 or older in 2004. Although ICD-9 code 287.3 is not exclusive to ITP, its sensitivity and specificity are likely to be high (Segal et al., Am J Hem. 2004). A patient’s first identified 287.3 ICD-9 code over the period 2002–2006 had to be in 2004 or earlier and the last one in 2004 or later. Patients had to have continuous enrollment throughout the year 2004. We estimated the 2004 prevalence as the total number of identified chronic ITP cases divided by the total population in the database in 2004 stratified by age group and gender. Estimates of adult cases for the US population were obtained by multiplying the 2004 prevalence estimates by the 2005 adult US census population estimates. The estimated adult prevalence was 23.6 [95% CI 23.4 – 23.8] per 100,000 persons, translating to approximately 52,700 (95% CI 52,200 – 53,100) adult chronic ITP cases in the US. Females had higher prevalence than males (28.1 vs 18.8 per 100,000). In addition, prevalence increased with age (from 17.0 in the age group 18–49 to 36.2 in the age group 65 and older). These results are broadly similar to previously published data and help to better understand the epidemiology of chronic ITP. While the tight CIs predominantly reflect the large data set rather than the precision of the estimates, we believe these data are among the most robust estimates of ITP prevalence and are the first to specifically estimate adult chronic ITP prevalence by age and gender in the US.