On call

Blood pressure in both arms

Q. My doctor usually checks my blood pressure in my left arm. When I went for my checkup yesterday, he used my right arm, and the reading was 10 points higher than usual. I asked him to check my left arm, and it was 8 points lower. Does the difference matter? And which is my real pressure?

A. Blood pressure readings vary from day to day, even minute to minute. They also vary from arm to arm, even when both arms are checked simultaneously. The difference is usually just a few millimeters of mercury (mm Hg, the standard unit for measuring blood pressure), but various studies report that 10% to 39% of people have a disparity of 10 mm Hg or more. More often than not, the readings are higher in the right arm than the left. Your blood pressure readings put you in good company, and your right-left disparity is nothing to worry about.