June 29, 2009 -- New research suggests that approximately one in six adults exhibit "white-coat" hypertension, meaning that their blood pressure is high when their doctor checks it, but normal the rest of the time.
Additionally, close to one in 10 people have a less well understood condition known as "masked" hypertension, in which blood pressure readings are normal in the medical setting but sporadically high in real life.
Both conditions have been thought by many to have little relationship to true hypertension risk, but the new study finds otherwise.
Participants with white-coat hypertension at the start of the study had more than double the risk of having sustained hypertension a decade later, compared to those with normal blood pressures. Those with masked hypertension had a 78% higher chance of developing sustained high blood pressure readings over time.
The study is the first to show that white-coat hypertension and masked hypertension are associated with clinically meaningful high blood pressure, which is a major risk factor for heart attack and stroke.
"This means that these conditions are by no means clinically innocent, as they have often been thought to be," study researcher Giuseppe Mancia, MD of the University Milan-Bicocca says in a news release.
White-Coat Hypertension Is Common
The study by Mancia and colleagues included 1,412 adults (aged 25 to 74) followed for 10 years in an ongoing health trial.
In addition to blood pressure readings obtained in the clinical setting, readings were also obtained with two widely used out-of-office tests -- ambulatory monitoring, which involved automated testing every 20 minutes over a 24-hour period, and sporadic home monitoring, using a lower-tech portable monitoring device similar to those available for purchase in drug and medical supply stores.
After 10 years, more than 40% of study participants who originally had white-coat hypertension or masked hypertension developed sustained high blood pressure readings, compared to 16% of those with normal blood pressures at the start of the study.
After adjusting for age and sex, the researchers concluded that the risk of developing sustained hypertension was 2.5 times higher in the white-coat group and 1.8 times higher in those with masked hypertension.
The study appears in the August issue of the American Heart Association (AHA) journal Hypertension.
Cardiologist Richard Stein, MD, tells WebMD that the study offers good evidence that white-coat hypertension and masked hypertension are clinically relevant.
Stein is a professor of medicine at New York University and a spokesman for the AHA.
Getting an Accurate Reading
Stein says patients who think their in-office blood pressure readings may be too low or too high should check their blood pressure at home.
Home monitors can be purchased for as little as $20, but it is a good idea to bring the device to your doctor's office to make sure that it is accurately calibrated.
He recommends that his heart patients with suspicious in-office readings test their blood pressure twice a day for a week before being checked again in his office.
"They will come in with about 14 readings, which gives me a better idea of what is going on than one or two readings in the office," he says.
Tips for getting an accurate reading at home include:
- Avoid caffeine, tobacco, or medicines known to raise blood pressure (such as nasal decongestant sprays) for at least 30 minutes before testing,
- Avoid exercise for at least 30 minutes before testing,
- Sit quietly with both feet on the floor (not crossed) for at least five minutes before taking your blood pressure.
- Check the blood pressure cuff frequently to make sure the rubber tubing, bulb, valves, and cuff are in good condition. Even a small hole or crack in the tubing can lead to inaccurate results.
Most people with consistently high doctor's office blood pressure readings (140/90mmHg or above) do have clinically meaningful high blood pressure, but others don't.
If you get particularly anxious or nervous when you visit the doctor, and your blood pressure is between 140/90 mmHg and 160/99 mmHg in this setting, you may have white-coat hypertension.
For the best chance of a good blood pressure reading in the clinical setting, try deep breathing, meditation, or other stress-reducing measures before visiting the doctor.
Make sure your feet are not crossed when your pressure is being tested; crossing your feet causes blood pressure to rise. It is also helpful to breathe in slowly and deeply and breathe out through pursed lips during testing.