Impact of risk factors on the occurrence of arterial thrombosis and venous thromboembolism in adults with primary immune thrombocytopenia - Results from two nationwide cohorts

Background: Previous studies have found that patients with Immune thrombocytopenia (ITP) have an increased risk of arterial thrombosis (AT) and venous thromboembolism (VTE). However, risk factors for thrombosis in adults with primary ITP remain unassessed in large cohorts. Aim To assess the occurrence and impact of risk factors for AT and VTE in patients with primary ITP in France and Sweden. Methods: Both countries have national health databases, including hospital diagnoses and drug dispensing data. Adults with incident primary ITP identified using algorithms between the years 2009-2015 in France, and 2009-2016 in Sweden were included. Cumulative incidence rates (IR) of AT and VTE were calculated by risk factors and multivariable Cox models were used to estimate associations. Results: The study included 7225 patients from France and 2490 from Sweden. The IR of AT were 15.0 (95% CI: 13.4-16.7) and 14.7 (95% CI: 12.4-17.5) per 1000 person-years, respectively. The incidences of VTE were 6.9 (95% CI: 5.9-8.1) and 6.5 (95% CI: 5.1-8.4), respectively. Increasing age, male sex and a previous AT were associated with AT in both countries and so were exposure to antiplatelet drugs in France and a history of VTE and chronic kidney disease in Sweden. Increasing age and a history of VTE were associated with VTE in both countries, in France also cancer. Conclusion: The IR of AT and VTE were similar in France. Age and male sex remained the most important risk factors for AT, age for VTE.