Levels of prolactin in relation to coagulation factors and risk of venous thrombosis. Results of a large population-based case-control study (MEGA-study).

The pituitary hormone prolactin is thought to influence coagulation. We aimed to study the relation between prolactin levels, coagulation factors and risk of venous thrombosis (VT). We used data from a large population based case-control study into aetiology of first VT (MEGA-study). Prolactin levels were determined in 2,068 patients with VT and 2,785 age- and sex matched control subjects. The relation between levels of coagulation factors and prolactin was studied among the controls. In addition, odds ratios (OR) and 95% confidence intervals (95%CI) were calculated for the risk of VT for different cut-off points of prolactin levels based on percentiles determined in the controls. Restricted analysis was performed among cases in whom blood was sampled within six months after VT. We found a rise in factor VIII and von Willebrand factor with increasing levels of prolactin in the controls. An increased risk of VT was observed when blood was sampled within six months after thrombosis (OR 2.9, 95%CI 1.1-8.1) for prolactin levels above the 99th percentile (42.6 μg/l) relative to levels between the 20th to 80th percentile. When blood was sampled more than six months after VT no clear association could be observed (OR 1.3, 95%CI 0.7-2.3). In conclusion, we found a modest association between prolactin and symptomatic venous thromboembolism, particularly when blood was sampled close to the event. This may be explained by a causal relation or by prolactin being a marker of stress due to the thrombotic event.