MacCallum PK, Ashby D, Hennessy EM, et al. Cumulative flying time and risk of venous thromboembolism. Br J Haematol 2011. doi:10.1111/j.1365-2141.2011.08899.x.
Conclusion: Compared with not flying, cumulative flying times > 12 h within the previous 4 weeks and > 4 h in a single leg are associated with three-fold and two-fold increases, respectively, in the risk of venous thromboembolism (VTE). These risks are no longer evident by 12 weeks. Risks associated with minor-, moderate-, and high-risk surgery are greater, with odds ratios (ORs) of 5.35, 36.57, and 141.71, respectively. The risks of VTE in those with a high baseline risk due to surgery, previous VTE, or obesity are further increased by air travel, reaching a predicted OR ~2,000 if all risks are present. Short-term anticoagulation with low molecular weight heparin could be considered in addition to other preventive measures in certain high-risk individuals.