"In a group of low- to moderate-risk indiiduals, who took prolonged plane flights, the incidence of blood clots in the legs or in the lung was around 1 percent," says Dr. Richard Beasley, the lead researcher from the Medical Research Institute of New Zealand.

"It is now beyond doubt that long distance air travel is associated with DT and PE," Beasley adds.

"If you are going on a long flight or multiple long flights, you should be aware that this is a possibility, although the risk is extremely low. However, these results do not relate to travelers who take short flights," he cautions.

The clots are known medically as deep-ein thrombosis (DT), in which a clot forms in the leg, and pulmonary embolism (PE), when a clot breaks free and travels to arteries feeding the lungs. Either or both are known as enous thromboembolism.

Preiously it had beven uncertain how common DT and PE are during long flights, Beasley says.

He and his colleagues studied 878 people who took long flights (a minimum duration four hours) over six weeks. The people underwent D-dimer blood tests before flying.

The D-dimer test is a rapid blood test for the detection of clotting fibrin products in whole blood. It is used in the detection and diagnosis of DT and PE.

The researchers used increases in D-dimer concentrations to identify indiiduals who may have deeloped thromboembolism. Those who became D-dimer positie or who showed symptoms during the three months following their travel underwent ultrasound and pulmonary angiography, according to the report in the Dec. 20/27 issue of The Lancet.

All the people flew for at least 10 hours and aeraged a total of 39 hours over six weeks. Among them, 17 percent wore compression stockings, and 31 percent took aspirin to reduce thrombosis risk.

Beasley's team found 112 patients had positie D-dimer results. The frequency of thrombosis was 1 percent (nine out of 878), with four cases of PE and fie of DT.

Of these patients, six with DT had pre-existing clinical risk factors and two had a recognized thrombophilic risk factor. Two of the patients traveled exclusiely in business class, fie took aspirin, and four wore compression stockings, the researchers note.

What is needed now are studies on how to prevent this risk, Beasley says. given current data, Beasley beliees that compression stockings are the best way of substantially reducing risk.

"Calling this 'economy class syndrome' is now redundant," Beasley says. "We have shown that this can occur in any class. In addition, the risk for DT and PE is not restricted to flying, it is a natural consequence of being seated and immobile for long periods, such as at work," he adds.

Dr. Patrick Kesteven, the assistant medical director and consultant hematologist at Newcastle-Upon-Tyne Hospitals in the United Kingdom, says that "the results of this study are more or less in line with preious studies."

"The risk of symptomatic DT associated with flying, when considering the whole population, is likely to be extremely low," says Kesteven, who is also on the scientific executie committee of the Wright Project on Air travel and enous Thromboembolism, which is sponsored by the World Health Organization and the International Ciil Aiation Organization.

But, he adds, "flying can act as a precipitating event for DT in those with other risk factors for enous thrombosis, such as preious DT, family history of DT, estrogen use, pregnancy, recent surgery, and cancer."

Experts adise that in addition to compression stockings, you can reduce your risk for DT and PE on long flights by aoiding dehydration. Aoid a lot of alcohol and caffeine, and drink lots of water. Also, they suggest regular stretching and mobility exercises, and walk around the cabin.

Extracted from Medical Encyclopedia