Thromboembolic events among adult patients with primary immune thrombocytopenia in the United Kingdom General Practice Research Database

The risk of thromboembolic events in adults with primary immune thrombocytopenia has been little investigated despite findings of increased susceptibility in other thrombocytopenic autoimmune conditions. The objective of this study was to evaluate the risk of thromboembolic events among adult patients with and without primary immune thrombocytopenia in the UK General Practice Research Database. Using the General Practice Research Database, 1,070 adults (>or=18 years) with coded records for primary immune thrombocytopenia first referenced between January 1(st) 1992 and November 30(th) 2007, and having at least one year pre-diagnosis and three months post-diagnosis medical history were matched (1:4 ratio) with 4,280 primary immune thrombocytopenia disease free patients by age, gender, primary care practice, and pre-diagnosis observation time. The baseline prevalence and incidence rate of thromboembolic events were quantified, with comparative risk modelled by Cox's proportional hazards regression. Over a median 47.6 months of follow-up (range: 3.0-192.5 months), adjusted hazard ratios of 1.58 (95% CI, 1.01-2.48), 1.37 (95% CI, 0.94-2.00), and 1.41 (95% CI, 1.04-1.91) were found for venous, arterial, and combined (arterial and venous) thromboembolic events, respectively, when comparing the primary immune thrombocytopenia cohort with the primary immune thrombocytopenia disease free cohort. Further event categorization revealed an elevated incidence rate for each occurring venous thromboembolic subtype among the adult patients with primary immune thrombocytopenia. Patients with primary immune thrombocytopenia are at increased risk for venous thromboembolic events compared with patients without primary immune thrombocytopenia.