An early warning system can help doctors prevent many cases of deep-vein thrombosis, the so-called "economy-class syndrome" that causes potentially fatal blood clots, researchers said.

Millions develop the clots each year, usually because of inactivity, cancer or dehydration. The condition has also been known to afflict passengers on long airline flights

Although the clots often develop in hospital patients who can not move around, doctors frequently do not take essential steps to prevent them.

A study published in this week's edition of The New England Journal of Medicine tested an experimental computer alert system at Brigham and Women's Hospital in Boston.

The computer program, linked to the hospital's patient database, identified more than 2,500 patients at risk of developing DVT and who may have needed preventive care, such as anti-coagulant drugs.

The program randomly assigned roughly half of the patients to an intervention group in which doctors were warned of their risk for developing DVT, and the remaining patients to a control group in which no alert was issued.

Study co-author Samuel Goldhaber and his colleagues found that more than twice as many people got treatment as a result of the automated alerts, producing a 41 percent decrease in the risk of either a deep-vein thrombosis or a lung embolism, which is caused when a clot lodges in the lung.

"We can definitely improve the quality of life of those who don't get (a clot) so they don't have the leg pains, the shortness of breath," Goldhaber stated.

Although Brigham and Women's issued a statement saying the alert system had the potential to save thousands of lives, the researchers were not able to conclusively prove this. Goldhaber said the number of patients involved may have been too small to detect a significant reduction in the death rate.

Still, he said such clots are "by-and-large preventable," and that the study results may spur other hospitals to take similar steps to identify and treat at-risk patients.

In an editorial in the Journal, Pierre Durieux of the George Pompidou European Hospital in Paris said the test illustrates the benefits of automated alerts for doctors.