Take Blood Pressure in Both Arms, Study Says Doctors who make a habit of measuring blood pressure in only one arm may be doing their patients a disservice. A new study shows that differences in blood pressure readings between a patient's right and left arm could be a sign of vascular disease and a greater risk of dying from heart disease. The study, published in The Lancet, suggests doctors should always take blood pressure readings on both arms - an existing guideline that is widely ignored. "Recommendations to measure both arms exist in both British and American blood pressure management guidelines," said Dr. Christopher Clark, the lead author of the study and a clinical academic fellow at the Peninsula College of Medicine and Dentistry in England. This is out there as guidance, but it's guidance that isn't regularly followed. In Britain, fewer than half of all doctors say they make a habit of measuring blood pressure in both arms, Dr. Clark said, a statistic that is likely to be similar in the United States. The consequences could be significant. In their study, Dr. Clark and his colleagues pooled data from their own research and from about two dozen other studies looking at differences in systolic blood pressure readings between the two arms in patients. Systolic pressure, the top number in a reading, reflects the amount of pressure that blood exerts on vessels while the heart is contracting. Although seemingly minor, a difference of 15 millimeters of mercury or more between systolic readings in the two arms meant the risk of peripheral vascular disease was two and a half times greater and the risk of cerebrovascular disease was 1.6 times higher. It was also associated with a 70 percent greater risk of dying from heart disease. The precise number of the higher or lower systolic reading was less important than the extent of the difference between them. A difference of even 10 millimeters was enough to raise the risk of peripheral vascular disease. The authors hypothesized that different blood pressure readings in the two arms were a sign of the narrowing or hardening of a person's arteries, particularly on one side of the body. Dr. Clark said the need for measuring blood pressure in both arms was clear. "If we don't know to measure both arms, we're not going to make the right diagnosis and the right treatment choices for our patients," he said. If you measure an arm where the blood pressure is lower than the other arm, you may be falsely reassured that the blood pressure is normal or is being adequately treated, when in fact the blood pressure is still high.