Blood pressure readings-Does the left arm know what the right arm is doing?

It’s common for blood pressure readings in one arm to be a bit different from those in the other, with readings slightly higher in the right arm. That’s why many public health organizations recommend that people have their blood pressure tested in both arms during their first visit to a healthcare provider, and that the arm with the higher reading be used in taking all future blood pressure measurements.

Blood pressure can differ between the two arms as a result of blockages in one arm’s arteries, but differences in pressure can also occur in people with no arterial disease. Blood pressure is notoriously variable, so many readings must be taken in consistent ways to determine whether the difference in pressure from arm to arm  signals a health problem.

Contrasting measurements
A recent study of 147 people being treated at a hypertension clinic in New York City examined  the issue of inter-arm difference in blood pressure readings (both the systolic pressure, when the heart contracts, and the diastolic pressure, when the heart rests between contractions).

Step 1: The doctors measured blood pressure in both arms simultaneously with a device different from the mercury thermometer you usually see in your doctor’s office.  
Step 2: They then checked blood pressure using the standard mercury thermometer three times on one arm and three times on the other.
Step 3: Finally, they took blood pressure readings again as in set 1, with the measurement devices on the opposite arm.
All three sets of measurements were repeated in 91 of the men and women during a second visit to the clinic.

The doctors found a small difference (but not significant in terms of the person’s health) in systolic and diastolic blood pressures in the arms of people without arterial disease. The inter-arm difference in systolic blood pressure was only significant in people with obstructive arterial disease.

The findings suggest that differences in blood pressure between arms of as much as 10 millimeters of mercury (mm Hg) are almost always due to random variation and can be safely ignored. If you have a marked and persistent difference in blood pressure between your two arms, however, you and your doctor may want to arrange a test for arterial disease.