This is true. It is possible that your blood pressure can be normal in the doctor’s office even though it is high elsewhere. This phenomenon is the opposite of white-coat hypertension – blood pressure that reads high in medical settings because of anxiety, but is otherwise normal. A new study from Stony Brook University and Columbia University found that nearly 16 percent of 888 working, middle-aged participants who agreed to wear ambulatory blood pressure monitors for 24 hours turned out to have “masked hypertension.”
Researchers reported that this problem was more common among the men in the study and among those participants who had prehypertension – “high normal” blood pressure that affects some 25 percent of U.S. adults. With prehypertension, your systolic pressure (the top number) is between 120 and 139 millimeters of mercury (mmHG) over 80 to 89 mmHG. Hypertension is 140/90 mmHg or higher.
The study also revealed that younger, normal-weight participants were more likely to have higher blood pressure readings via ambulatory monitoring than they did in the doctor’s office. The average age of the participants was 45. More than half were women. Most participants were white, seven percent were African-American and 12 percent were Hispanic.
The only way to determine whether or not you have masked hypertension is to wear a portable blood pressure monitoring device for 24 hours. On entering the study the participants had three separate blood-pressure readings taken during each of three clinic visits and then wore the monitor for one 24-hour period. During that time, readings were taken automatically about every 30 minutes.
The study revealed that health care professionals can easily miss patients with masked hypertension. However, study leader Joseph E. Schwartz Ph.D. of Stony Brook University said in a press release that accompanied publication of the study that the results may not apply to those who have previously been diagnosed with hypertension or are already being treated for it. The researchers said their results must be confirmed in further studies with more diverse populations. It may also turn out that wearing a blood pressure monitor may influence blood pressure much the same way a “white coat” does for some patients.
Masked hypertension also showed up in earlier studies during which participants had ambulatory blood pressure monitoring. In those investigations, from 10 percent to 40 percent of participants were found to have masked hypertension, and in follow up studies 47 percent of those with masked hypertension eventually developed high blood pressure.
Masked hypertension could put you at higher than normal risk of cardiovascular problems including stroke. Since high blood pressure generally doesn’t cause symptoms, having it measured periodically is a good preventive strategy. If readings are high in a medical setting, check it yourself at home. Reliable automated electronic devices for this are available online and at most pharmacies; they cost between $50 and $100. Check your blood pressure at random times, three or four times a day. Keep a log of the readings for a month and share them with your doctor during your next appointment.
Andrew Weil, M.D.
Joseph E. Schwartz et al, “Clinic Blood Pressure Underestimates Ambulatory Blood Pressure in an Untreated Employer-Based US Population.” Circulation, December 5, 2016; 134 (23): 1794 DOI: 10.1161/CIRCULATIONAHA.116.023404
Giuseppe Mancia et al, “Long-term risk of sustained hypertension in white-coat or masked hypertension.” Hypertension, August 2009, doi: 10.1161/HYPERTENSIONAHA.109.129882