The findings, published online December 21 in the newspaper Hypertension, are based on 24 studies worldwide, involving almost 54,000 adults in all. Over 10 years, 11% had a fatal or non-fatal heart attack or stroke.
It is normal, Clark said, to have some points of variation in blood pressure between the two arms – due to anatomy and the fact that one hand is typically dominant.
“Our interest was in identifying when that difference is big enough to be considered to mean more than that,” said Clark. “When is the difference large enough to suggest a change in arteries that could mean an additional risk of stroke or heart attack?”
Overall, his team found, people’s risks started to rise when both arms showed a difference of at least 5 points in systolic blood pressure (the “main” number in a blood pressure reading).
For every 1 point increase, the risk of dying from heart disease in the next 10 years increased by 1% to 2%. Meanwhile, the chances of suffering a first heart problem or stroke have also increased.
These increases were small, but the researchers said a 10-point difference in systolic pressure between the arms should be considered the “upper limit of normal”.
Differences between arms are more common in people with high blood pressure, Clark said, but people with normal readings may also have them.
The phenomenon is more important for those with high blood pressure or other risk factors, such as diabetes and high cholesterol, he added.
Berger said it is not clear why so few health care professionals measure blood pressure in both arms.
“This is not a new discovery,” he said of the current study. “It has been shown many times.”
For now, Berger suggests that patients ask questions the next time they do a blood pressure check: If it’s not being done on both arms, why not?
As for home blood pressure monitoring, he said, if people repeatedly detect a significant difference between the arms, they should tell the doctor.
Clark was also in favor of doctors checking both arms at least once – in part to get a more accurate measurement of patients’ blood pressure. If an arm has a higher reading, he said, then future measurements should be made on that arm.