A difference of 10 or more points could signal peripheral artery disease.
Roll up both sleeves the next time you check your blood pressure at home or have it measured by a health care provider. Why? A recent analysis of 20 different studies in which blood pressure was measured in both arms came to two noteworthy conclusions.
First, people with arm-to-arm pressure differences of 15 points or more were twice as likely to have peripheral artery disease (PAD) compared with those who had similar readings in both arms. PAD occurs when vessels of the arms, legs, or other body parts beyond the heart and brain become clogged, usually from atherosclerosis, the buildup of fatty plaque that is also behind most heart attacks and strokes.
Second, arm-to-arm pressure differences of 10 to 15 points or more also boosted the chances of having a stroke or dying from cardiovascular disease (The Lancet, published online Jan. 30, 2012).
Early warning sign
The first finding may be more worthy of attention than the latter, even though strokes and death sound more grievous than "peripheral artery disease." The fact is that PAD affects an estimated 12 million Americans—more than heart disease and stroke combined. It can severely limit mobility and cause debilitating pain, but it can also lurk silently. It can be deadly as well, which might make differences in blood pressure from arm to arm an important early warning sign.
Most guidelines already recommend measuring blood pressure in both arms, but many doctors and do-it-yourselfers ignore that guidance. You needn't worry much about variations of a few points between the right and left arm. But if your arm-to-arm readings at home (see box) diverge by more than 10 or 15 points, tell your doctor and ask him or her to check both arms also.
If your doctor finds the same discrepancy, he or she might order another test. That's the ankle-brachial index, which is calculated from blood pressure measurements at the ankle and the arm. Pressure that is significantly lower at the ankle than at the arm suggests a blockage in the leg. And, as the authors of a commentary accompanying the Lancet article note, many cases of high blood pressure could be missed when only one arm is checked.
Tips for accurately measuring blood pressure at home
Avoid caffeine, alcohol, and nicotine for 30 minutes before you take the reading.
Sit quietly for a few minutes with your feet on the floor before inflating the cuff.
Rest your arm so your elbow is level with your heart, and wrap the cuff over the bare skin of your upper arm.
Take two readings. If they're close, average them. If not, take a third reading and average the three.
Repeat the procedure in the other arm.
For a video showing how to measure your blood pressure at home, go to health.harvard.edu/128 or scan this code with your smartphone.
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