Investigators in the Netherlands evaluated the effects of air travel versus long periods of immobilization on the ground on indicators of clotting activation. Seventy-one patients were divided into 4 groups: (1) patients with the factor V Leiden (FVL) mutation, (2) patients who used oral contraceptives (OCs), (3) patients with both risk factors, and (4) patients with neither risk factor. Three indicators of clotting were measured at baseline and before and after 3 interventions: an 8-hr plane flight, an 8-hr movie marathon, and 8 hr of a "daily life situation."

Thrombin-antithrombin complex was the indicator that exhibited the greatest increase of ~30% after the flight, versus decreases of 2% and 7.9% after the movie marathon and the daily life situation, respectively. High responders for any of the indicators were found in 17% of individuals after air travel, versus 3% after the movie marathon and only 1% after the daily life situation.

The presence of FVL or OC use increased the likelihood of having elevated indicators, and the effect of combining both factors appeared to be additive. The authors suggested that the low air pressure and/or low oxygen level in planes during travel may increase the risk of clotting over that observed with immobilization on the ground. Risks appear to be higher in patients with FVL or OC use but are not completely negated in patients with no risk factors. Two of the highest responders in the study had neither of the studied risk factors.

Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care in High Point, NC.