The incidence of venous thromboembolism in patients with overt hyperthyroidism: a retrospective multicentre cohort study.

Hyperthyroidism is associated with several changes in the haemostatic system resulting in a hypercoagulable state. It is uncertain at this stage whether this leads to an increased risk of venous thromboembolism (VTE). The aim of this retrospective cohort study was to determine the risk of VTE in all patients with overt hyperthyroidism and to compare this to the risk of VTE in the general population. In three hospitals in the Netherlands, patients with biochemically confirmed hyperthyroidism caused by Graves' disease, multinodular goiter or toxic adenoma were included. All available electronic and handwritten records were examined. Primary outcome was the occurrence of VTE within six months before and until six months after the diagnosis of hyperthyroidism. We included a total of 587 patients. Five patients experienced a VTE during the study period, resulting in an incidence rate of 8.7 (95% CI 2.8 - 20.2) per 1,000 person-years. Three of these five patients had a first VTE (incidence rate for first VTE was 5.3 [95% CI 1.1 - 15.6] per 1,000 person-years). Incidence rates of VTE in the general population are between 0.6 and 1.6 per 1,000 person-years for first VTE and 0.7 and 1.8 per 1,000 person-years for all VTE. In conclusion, the incidence rate of VTE in patients with hyperthyroidism appears to be high. Future prospective studies are needed to further explore this possible association and to address its clinical implications.