The Incidence of Idiopathic Thrombocytopenic Purpura (ITP) among Adults in the United Kingdom’s General Practice Research Database (GPRD), 1992–2005.

ITP is a disease caused by inadequate platelet production as well as increased platelet destruction. Population-based literature on the epidemiology of ITP is currently sparse, but incidence has been estimated to be between 1.6 and 3.0 per 100,000 person years of observation (PYO) (Neylon AJ et al., Br J Haematol. 2003; Satia J et al., Eur Hematol Assoc [poster presentation] 2006). The objective of this study was to estimate the incidence rate of ITP in adults in the United Kingdom using the GPRD, which contains patient data from over 370 representative medical practices. Using diagnostic codes for ITP (D313000, D313012, 42P2.11, or D313.12 or the Oxford Medical Information System code 2871C) to define cases, incidence rates per 100,000 PYO with 95% confidence intervals (CI) were estimated. Incidence by age, gender, and time period (1992–1998, 1999–2005) was evaluated. Eight hundred forty adult cases of ITP (aged 18 years or more) during 21.7 million PYO from 1992 to 2005 were identified. The overall incidence rate (per 100,000 PYO) during this time was 3.9 (95% CI: 3.6, 4.1) with higher rates among women (4.6 [95% CI: 4.2, 4.9]) compared with men (3.2 [95% CI: 2.8, 3.5]). Incidence rates (per 100,000 PYO) increased with age (from 2.5 [95% CI: 2.2, 2.7] to 4.1 [95% CI: 3.6, 4.6] to 8.2 [95% CI: 7.3, 9.2] in the age groups 18–49, 50–69 and 70+ respectively), and in later study years (from 2.9 [95% CI: 2.5, 3.2] in the period 1992–1998 to 4.5 [95% CI: 4.1, 4.8] in the period 1999–2005). In summary, ITP was diagnosed in approximately 4 adults per 100,000 PYO in the General Practice Research Database. Incidence rates of ITP in this study are slightly higher than in previous estimates, possibly due to a code-based disease definition without validation by clinical and lab data. More population-based studies of the natural history of adult ITP are needed to better elucidate the burden of this disease.