[新闻背景]Doctors generally check their patients' blood pressure during office visits, but a new study says many are not doing it the right way - and that by doing it incorrectly, the doctors could be putting their patients' lives at risk.

Cardiologist Oscar Garfein takes blood pressure readings from both of his patients' arms. That technique saved the life of one of his patients.

"I found that in one arm, it was very, very low, and in the other one, it was normal," says Garfein. "And it helped me arrive at a diagnosis of a potentially-lethal condition."

Garfein's routine is supported by a new study showing that different readings in the right and left arms could be a sign of heart disease or blood vessel problems. If the two readings of systolic blood pressure - the pressure of blood in arteries when the heart is contracting - differ by 15 or more, it could indicate a narrowing of arteries to the legs, decreased blood flow to the brain, heart disease and a 70 percent increased risk of dying from either heart attack or stroke.

If heart or blood vessel disease is diagnosed at an early stage, changing risky behavior or taking statin drugs can reduce death rates.

"You want to search for the risk factors that are associated with this," says Garfein, "such as high blood pressure or cigarette smoking or high cholesterol, and treat them very aggressively."

Many cardiologists routinely check blood pressure in both arms, but the practice is much less common on a routine doctor's visit. This study, published in The Lancet, confirms a double reading could flag an underlying vascular problem in someone who otherwise seems to be healthy.

The study shows it doesn't matter what the systolic number was, it's the difference between the two readings that matters.

"All it takes is about a minute and you can find something that really, most of the time, points to the fact that this patient has established vascular disease," says Garfein.