- The Washington Times - Thursday, December 18, 2003

PARIS (Agence France-Presse) — Deep-vein thrombosis may occur among one in every 100 frequent long-haul air travelers, says one of the most detailed studies of the health phenomenon.

The results point to a link between deep-vein thrombosis and multiple long-distance flights “even in individuals at low to moderate risk,” its British and New Zealand authors warn in the issue of the Lancet, a medical trade journal.

Deep-vein thrombosis is the term for a blood clot that forms in leg veins during long periods of sedentary activity. The clot can migrate to the heart, lung or brain, inflicting a heart attack or stroke.

The researchers recruited 878 volunteers ages 18 to 70 who traveled at least 10 hours by plane over six weeks. The average was 39 hours of travel during this period.

The recruits were measured for a blood protein called D-dimer, which is linked to dangerous clotting, both before and after their flight.

Individuals with higher levels of D-dimer after the flight, or who developed symptoms of deep-vein thrombosis in the three months after travel, were given an ultrasound scan and lung X-ray.

Nine out of the 878 volunteers — or 1 percent — developed deep-vein thrombosis. Five had leg clots while the other four had clots that had reached their lungs.

Six out of the nine had pre-existing risk factors for deep-vein thrombosis.

What struck researchers was how deep-vein thrombosis occurred among people who had taken precautions against clotting, such as using aspirin to thin the blood or wearing compression stockings to improve circulation in the legs.

Two of the nine traveled exclusively in business class, thus giving the lie to the common belief that deep-vein thrombosis occurs only among those in the cramped, cheaper seating.

Deep-vein thrombosis has been known since World War II, when it was noted among Londoners who spent long hours sitting on deck chairs in underground air-raid shelters.

Its frequency is unknown, and most studies are based on data such as hospital admissions rather than from clinical evidence and personal follow-up checks.

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