The Prevalence of Immune Thrombocytopenic Purpura (ITP).

Introduction: Knowing the prevalence of ITP is important to determine the burden of this rare disease. Multiple new thrombopoietin agonists are being developed for the treatment of ITP, despite the paucity of reliable and generalizable estimates of ITP prevalence. Only two studies have previously reported the prevalence of ITP in the United States (US) (the only other prevalence estimate focused on children with chronic ITP in the United Kingdom).

Methods: Similar to the previous 2 studies, the ICD-9-CM code of 287.3 was used to identify ITP. Unlike the previous 2 studies, we obtained data directly and entirely from hematologists. In November 2007, there were 93 hematologists in Oklahoma who cared for ITP patients. Our preliminary data documented that hematologists saw ³ 92% of all patients with ITP and that primary care physicians in Oklahoma reported they were ‘likely’ to refer 85% of patients with platelet counts <30,000/μL and bleeding symptoms to a hematologist. All hematologists were asked to provide information on all (new and existing) ITP patients seen from 01/01/2003–12/31/2004. Ninety-five percent (88/93) of the hematologists in the state were able to provide these data. One-year prevalence estimates were used to generate an annual average prevalence. Prevalence estimates were calculated separately for children (age <16 years), adults (age > 16 years), and the overall population. The denominator was the Oklahoma population (US Census 2000).

Results: The 2003 prevalence estimates were: 8.8 per 100,000 children, 11.6 per 100,000 adults, and 11.0 overall per 100,000 persons. The 2004 prevalence estimates were: 7.4 per 100,000 children, 12.6 per 100,000 adults, and 11.4 overall per 100,000 persons. The average annual prevalence estimates were: 8.1 per 100,000 children (95% CI 6.7, 9.5), 12.1 per 100,000 adults (95%CI 11.1, 13.0), and overall 11.2 per 100,000 persons (95% CI 10.4, 12.0). The children were 51% female, 49% male, and the average age was six years. Adults were 57% female, 43% male, and the average age was 55 years.

Conclusion: This is the first population based study to determine the prevalence of ITP for an entire defined geographic region, regardless of insurance status and age. These results represent the most generalizable estimates of prevalence currently available on which to determine the burden of ITP. Results from this study should be generalizable because the demographics of Oklahoma closely resemble the demographics of the US. Additionally, these results confirm and extend the previously published prevalence estimate of Segal et al, 2006. This information is important not only for pharmaceutical companies, regulatory agencies, and heath care authorities, but also for patients with ITP.