Risk up with flight but fatal clots rare

Air travellers are in danger of suffering blood clots but the risk is small, a study shows. Picture / Amos Chapple

Long-distance air travel increases the risk of dying from blood clots in the lungs, a new study has found.

Otago University researchers have found that people who flew for more than eight hours were eight times more likely to die from pulmonary embolism than non-travellers - even when risk factors such as obesity, medical conditions and the use of medications were taken into account.

But researchers also found the potentially fatal condition to occur relatively rarely.

The Health Ministry funded the two-year study that looked at people who had died from pulmonary embolism and a comparison group drawn from electoral rolls.

Dr Lianne Parkin, a member of the research group, said New Zealand was ideal to undertake this study, as almost all overseas travellers had to fly for at least three hours.

"One reason for undertaking this study was that air travel was commonly believed to increase the risk of developing deep-vein thrombosis, but there was very little information about the risk of dying from pulmonary embolism following a long-distance flight."

To obtain their findings, researchers studied 121 deaths of New Zealand residents and visitors aged 15 to 59 between January 1, 1990, and December 31, 2000, whose deaths were associated with blood clots. Of those, 11 people (9 per cent) had undertaken long-distance air travel in the four weeks leading up to their death. Seven had no history of blood clotting, while two others had unknown histories.

Researchers also obtained data from Statistics New Zealand in order to estimate the absolute risk of fatal pulmonary embolism in air travellers.

Dr Parkin said that for every million people aged 15 to 59 years who flew for more than eight hours, one person died from pulmonary embolism.

"This is a much lower risk than publicity about the so-called economy-class syndrome has led many people to believe."

Although the study did not look at reducing the risks of pulmonary embolism, there were possible benefits from wearing well-fitted support stockings, particularly for those who had a strong family history of blood clots, said Dr Parkin.

"People who believe they may have a particularly high risk and are concerned about air travel might like to talk to their doctor about possible preventive measures."

Qantas and Air New Zealand declined to comment on the study.

Pulmonary embolism

* A sudden blockage in a lung artery, usually due to a blood clot that has travelled from the leg.

* If the clot is large, or there are many clots, pulmonary embolism can cause death.

* The most common sources of embolism are proximal leg deep-vein thrombosis (DVTs) or pelvic vein thrombosis.

* Any risk factor for DVT also increases the risk that the clot will dislodge and migrate to the lung.