Where Your Blood Pressure Is Taken Can Make a Difference

Blood pressure readings are a routine part of doctor visits, and you're likely familiar with the most common reading method: an expanding and contracting cuff wrapped around your arm. But is blood pressure measured from your leg any different? And why choose one spot over another?

Blood pressure readings are generated as two numbers: a systolic (top) number and a diastolic (bottom) number. The Mayo Clinic explains that systolic refers to the maximum pressure the heart exerts while beating, whereas diastolic refers to arterial pressure between beats. A top reading below 120 coupled with a bottom reading below 80 is considered "normal." But when the top number edges above 120 or the bottom one creeps upwards of 80, it's a sign of potential trouble.

A 2019 scientific statement issued by the American Heart Association (AHA) stressed the importance of ensuring that blood pressure measurements are accurate. But there are many factors that can affect results, and reading location is one of them. For example, Johns Hopkins Medicine cautions that readings taken at the wrist or by finger, while feasible, produce less reliable results than arm reading.

Also, studies have shown that upper and lower extremity blood pressure differences do exist. In April 2019, the Journal of Hypertension published a review of 44 prior investigations that identified large discrepancies between arm readings and ankle readings.

Among healthy people, the review found no difference in diastolic (bottom number) arm readings versus ankle readings taken in a lying-down position. However, ankle readings produced systolic results that were 17 points higher than arm readings. And complicating matters, among people with vascular disease, ankle readings produced top numbers that were about 33 points lower than arm readings.

Read more: What Is Normal for Blood Pressure?

"Normally, leg readings will tend to be higher, but really leg and arm readings should roughly be the same," notes John Osborne, MD, PhD, a spokesperson for the American Heart Association and a cardiologist with State of the Heart Cardiology in Fort Worth, Texas.

But underlying disease can affect results. For example, blood vessel constriction triggered by peripheral arterial disease can result in significantly lower blood pressure readings in the leg versus the arm, says Dr. Osborne. And a congenital malformation of the aorta can produce significantly higher readings in the arm than the leg.

Taking all that into account, the AHA's 2019 statement explicitly came down in favor of the upper arm for blood pressure readings, by means of an automated electronic pressure sensor (oscillometric) equipment and an arm cuff.

Still, the American Association of Critical-Care Nurses (AACN) cautions that measuring BP is not one-size-fits-all. There are several patient and provider variables to consider. AACN advises that patients need to be evaluated for complication risks, such as bruising and skin irritation resulting from cuff pressure around the reading site.

Of particular concern, according to AACN, are people with underlying heart disease or diabetes who undergo frequent blood pressure readings. Though it's relatively rare, they may end up developing pain, swelling (limb edema), vein inflammation (phlebitis) or even a blood clot (thrombophlebitis) at a repeatedly used reading site.

Read more: How to Quickly Lower Your Blood Pressure

Such health considerations could mean that a leg reading is the better way to go, explains Dr. Osborne.

"For example, sometimes we run into patients who have undergone a surgical procedure to remove some of their lymph nodes," he notes. "Very often women, in particular, have had such surgery in the arm pit. And that surgery can cause lymphedema, which is a swelling of the arms. And in that situation you want to be very careful about not taking blood pressure in the arms, because it can aggravate the swelling and be painful."

People who have kidney disease can present a similar challenge, Dr. Osborne says, "because you don't want to wrap a blood pressure cuff around the same extremity being used for a dialysis connection."

And there's yet another reason to opt for the leg, notes Kenneth A. Ellenbogen, MD, a professor of cardiology and chair of the division of cardiology at the Virginia Commonwealth University Heart Center in the Medical College of Virginia School of Medicine in Richmond — to diagnose peripheral arterial disease.

"We measure blood pressure in the leg when we are looking for evidence of peripheral arterial disease," Dr. Ellenbogen explains, because if the pressure in the arm is greater than in the leg, it suggests a blockage in the artery to the leg."