Most people who have high blood pressure in a doctor's office or a clinic should undergo "ambulatory monitoring" before a diagnosis of hypertension is made, according to new recommendations from the influential U.S. Preventive Services Task Force. This will greatly reduce the chances of misdiagnosing hypertension and unnecessarily treating it with medication, since studies have found that anywhere from 10 to 50 percent of people with elevated blood pressure readings in medical settings do not have high ambulatory results.
There are some exceptions: Notably, people with very high blood pressure (180/110 or higher) or chronic kidney disease should start drug therapy right away and don't need ambulatory testing to confirm a diagnosis of hypertension.
Ambulatory monitoring, ordered by a physician, calls for wearing a device that automatically measures blood pressure and stores the results every 20 to 30 minutes for 24 to 48 hours while you go about your daily activities and while you sleep.
Measurement of blood pressure in a medical setting may not be accurate because factors such as emotions, physical activity, and caffeine intake during the prior 30 minutes or so can affect the results. In particular, many people have "white coat hypertension"—that is, their blood pressure goes up because they feel anxious in the presence of medical personnel.
What's more, even in doctors' offices blood pressure is often measured in a less-than-optimal manner. For the most accurate results, for example, you should wait a few minutes in a quiet room before testing; the cuff should fit properly (cuffs come in different sizes) and not cover clothing; and blood pressure should be measured in both arms, at least at the initial visit. Sitting with your back unsupported or feet off the ground, crossing your legs, talking, or letting your arm hang too low (or holding it up by yourself) can raise blood pressure. For more tips, see Blood Pressure: Getting It Right.
Ambulatory blood pressure monitoring makes particular sense if you have mildly or moderately elevated readings in a medical setting—before you start taking hypertension medication, possibly for the rest of your life. If you’re already being treated for mild hypertension, ask your doctor if it would be a good idea to do ambulatory testing while you stop taking your drug.
Because ambulatory testing is not always available or affordable, the Task Force's final recommendations included home blood pressure monitoring as an alternative method for confirming the diagnosis of hypertension.
Originally published April 2015. Updated October 2015.