Risk of venous thromboembolism in first- and second-generation immigrants in Sweden

Background: There are ethnic differences in the incidence of venous thromboembolism. This is the first nationwide study to examine whether there is an association between country of birth in first-generation immigrants and first hospitalisation for venous thrombosis (VT) and pulmonary embolism (PE), and to study whether a similar association exists in second-generation immigrants.

Methods: The study is a nationwide follow-up study. The study subjects were first- and second-generation immigrants residing in Sweden between January 1, 1964 and December 31, 2007. The reference population comprised first- and second-generation Swedish-born individuals. Standardised incidence ratios (SIRs) for VT and PE, standardised with regard to age, geographic region of residence, time period, and socioeconomic status, were estimated by sex in first- and second-generation immigrants.

Results: First-generation male and/or female immigrants from Greece, Italy, Spain, Finland, Baltic countries, Central Europe, Eastern Europe, Russia, Latin America, Turkey, Iran, and Iraq had a lower risk of VT and/or PE than Swedish-born individuals. The lower risk of VT and/or PE in some first-generation immigrant groups was not replicated in the second generation. However, in certain second-generation immigrant groups, the risk of VT/PE was similar to that in the corresponding parental groups.

Conclusions: Country of birth affects the risk of VT and PE in several immigrant groups. Our study indicates that ethnicity-related inherited and acquired venous thromboembolism risk factors play a role in the aetiology of venous thromboembolism. Ethnic differences in thromboembolism risk even exist in Caucasian European populations, and may thus be important to consider in genetic studies.