Study supports air travel/VTE link

Air travel can put frequent or casual flyers at significantly increased for a venous thromboembolic event for up to a month after the end of a trip, British researchers reported at a meeting of the International Society on Thrombosis and Haemostasis.

Flying more than 4 hours at a stretch — or a total flying time of more than 12 hours in the past 4 weeks — was associated with a two to nearly threefold greater risk for venous thromboembolism (VTE), compared with nontraveling controls, as reported by The London at the University of London.

“In this community-based case-control study, it was found that air travel was a mild risk factor for venous thrombosis in the subsequent 4 weeks. The risk seen at 4 weeks was no longer apparent at the 12-week time-frame, so the dose response and the declining risk with the passage of time tend to support a casual relationship between air travel and subsequent thrombosis.”

The size of the air-travel effect on VTE-risk was comparable to that of low risk surgery. Other factors associated with increased VTE risk were body mass index from 25 to 30 kg/m2, or greater than 30.

Case series linking air travel to VTE risk date to the 1950s, and by 1977 the phenomenon had been dubbed “economy class syndrome”. Case control, observational, follow-up, intervention, and laboratory studies have been conducted in the past decade.

The current study findings echo those of a recent meta-analysis, which suggested that air travel was associated with about a threefold risk for VTE.

Studies were made on patients in 123 general practices in the United Kingdom. They identified patients who had received a prescription for warfarin over the previous 12 months, performed a record search to identify patients with confirmed deep vein thromboembolism/pulmonary embolism (DVT/PE), and assigned six age- and sex-matched controls for each case.

The researchers contacted cases and controls by mail, and received replies from 638 cases (55 percent) and 3,162 controls (58 percent). After exclusions for various reasons, they arrived at 550 cases and 1971 controls for the final sample (1:36 ratio).

In a univariate analysis, the only significant flight-associated risk factor for short-term VTE was total flight time longer than 12 hours. In a multivariate analysis adjust for BMI, surgery, and past history of VTE, the only significant risk factors for VTE within 4 weeks of flying were any flight leg longer than 4 hours and total flying time greater than 12 hours. By the week 12, neither flight leg duration nor total flight time was significantly associated with increased risk for VTE.