Sporadic high blood pressure deserves attention

Published: November, 2009

Different readings in the doctor's office and at home are cause for concern.

A single blood pressure reading, like the one made in your doctor's office, is merely a snapshot taken from an endlessly playing 24-hour movie. For some people, that one measurement is a good summary of the movie. For others, it's a poor reflection of their usual blood pressure.

As many as 20% of Americans have different blood pressure at home than they do in the doctor's office. Some have white-coat hypertension — high blood pressure in the doctor's office but normal pressure at home. Others have masked hypertension — normal blood pressure in the doctor's office but periods of high pressure at home, such as during episodes of stress or early in the morning when the effects of blood pressure medicine have worn off.

Some doctors shrug off these two conditions, while others take them seriously. Contradictory data have long supported both approaches. Now, a long-term study from Italy raises concerns that both of these situations deserve more attention.

Blood pressure categories



Normal (optimal)

less than 120


less than 80






140 or higher


90 or higher

Steady progression

In the early 1990s, several thousand residents of the northern Italian town of Monza agreed to take part in a study called Pressioni Arteriose Monitorate E Loro Associazioni. They had their blood pressure carefully measured in a doctor's office, wore a device that recorded their blood pressure every 20 minutes for 24 hours, and measured their blood pressure at home in the morning and evening on several days. These measurements showed that 16.1% of the volunteers had white-coat hypertension, 8.9% had masked hypertension, and 20.9% had sustained high blood pressure.

Ten years later, more than 1,400 of the volunteers repeated the process. During that period, 47% of those with masked hypertension and 43% of those with white-coat hypertension had gone on to develop sustained high blood pressure, compared with just 18% of those whose pressures were initially normal (Hypertension, August 2009).

Do this at home

This important study underscores what we have been saying for years: it's a good idea to check your blood pressure at home, and not just rely on the measurements made in your doctor's office.

Home blood pressure monitors are easy to use and inexpensive (some cost under $50 and may even be covered by your insurance if you get a doctor's prescription for it.) Measure your blood pressure in the morning before you take your blood pressure pills or have breakfast, and again in the evening, every day for a week. Write down the numbers, along with the heart rate the monitor records, and bring them to your doctor. After that, follow the plan your doctor recommends.

White-coat and masked hypertension suggest that your blood pressure is more mercurial than normal. This hyper-responsiveness could gradually nudge you toward sustained hypertension. If your blood pressure is sometimes high, doing what you can to keep it in check is a big step toward preventing heart attack, heart failure, and the most common kind of stroke.

As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.