People with normal blood pressure at the doctor's office but high blood pressure at other times may have a doubled risk of heart attacks and strokes, according to new research reviews.
In two analyses covering four industrialized countries and more than 5,000 people, researchers also found that home blood pressure monitoring frequently picks up that so-called masked hypertension.
If that leads to more people with hidden high blood pressure getting treatment, it would be affordable and worthwhile to expand home monitoring, they say.
"We know that a lot of cardiovascular complications occur in people who are normotensive if you measure the blood pressure in the regular way in the office," Dr. Jan Staessen told Reuters Health in an email.
Staessen, a researcher in the Division of Cardiovascular Diseases at the University of Leuven in Belgium, is senior author of the studies published in PLOS Medicine and Hypertension.
About 10 per cent of the general population has normal or high-normal blood pressure readings at the doctor's office, but they actually have high blood pressure at home or at work. This is known as masked hypertension and it often goes untreated because it's hard for doctors to detect.
To see how masked hypertension affects risk for cardiovascular events like heart attack and stroke, Staessen and colleagues analyzed data from five previous studies of home-monitored blood pressure done in Finland, Japan, Greece and Uruguay.
For the new study, blood pressure readings with a top number below 120 and a bottom number below 80 were considered "optimal." Normal blood pressure was a reading of 120-129/80-84, "high-normal" was 130-139/85-89, mild hypertension was 140-159/90-99 and severe hypertension was a top number of 160 or higher and a bottom number of 100 or more.
The researchers considered a home reading of 130/85 or above to indicate masked hypertension when the person did not meet the criteria for high blood pressure at the doctor's office.
By that standard, they found that 5 percent of those with "optimal" blood pressure at the clinic, 18.4 percent with "normal" clinic readings and 30.4 percent with "high-normal" clinic readings had masked hypertension at home.
During a median 8.3 years of follow-up, participants with masked hypertension had between 2.24 and 2.65 times the risk for cardiovascular events when compared to those with true normal blood pressure.
In a commentary published in PLOS Medicine, Dr. Mark Caulfield of Barts and The London School of Medicine and Dentistry points out that cardiovascular disease is the leading