Home blood pressure monitoring and ambulatory blood pressure monitoring -- two different ways to measure blood pressure outside a doctor's office -- are both effective methods to detect "masked hypertension," according to a study.

Masked hypertension is defined as high blood pressure that is not detected during testing in the clinical setting. The opposite of white-coat hypertension, masked hypertension means a person has normal blood pressure in the doctor's office but high blood pressure outside of the office.

"Masked hypertension has recently attracted great attention as a phenomenon with potential clinical significance," Dr. George S. Stergiou of Sotiria University Hospital in Athens, Greece and colleagues point out in the American Journal of Hypertension.

They conducted a study to determine the level of agreement between home blood pressure and ambulatory blood pressure measurements in identifying masked hypertension.

Both methods have important similarities in that they provide multiple blood pressure readings taken outside the clinic, the investigators explain. But they also have important differences in that the home blood pressure monitoring provides readings on different days in the sitting position at home, while ambulatory blood pressure monitoring provides 24-hour measurements in ambulatory conditions, at home, at work and during sleep.

All patients in the study had been referred to the clinic for evaluation of elevated blood pressure. Their blood pressure was tested at the clinic in two visits two to four weeks apart. Study participants also measured their own blood pressure on six routine workdays during a two-week period, and had 24-hour ambulatory monitoring over a routine workday.

A diagnosis of masked hypertension was based on clinic blood pressure below 140/90 mm Hg and awake ambulatory blood pressure or average home blood pressure of 135/85 mm Hg or above. Normal blood pressure is anything below 120/80 mm Hg.

Masked hypertension was uncovered in 62 or about 14 percent, of patients using ambulatory monitoring and in about 12 percent based on home measurements.

In 44 patients, ambulatory and home blood pressure measurements were in disagreement, with 27 having masked hypertension based only on elevated ambulatory BP, while 17 had elevated home readings only.

But among most of the patients for whom there was test disagreement, the blood pressure increase was less than 5 mm Hg.

Ambulatory and home blood pressure monitoring are "interchangeable" for identifying masked hypertension in most patients, the researchers conclude.

"It might be argued, however, that for the long-term follow-up of treated subjects with masked hypertension, home blood pressure monitoring is more appropriate than ambulatory monitoring," they say, "because of its lower cost and greater convenience for repeated measurements."

SOURCE: American Journal of Hypertension June 2005.