Prevalence and persistence of masked hypertension in treated hypertensive patients.

BACKGROUND Masked hypertension (MH) is defined as a normal blood pressure in the physician's office and an elevated blood pressure when measured out-of-office. The cause of MH may be termed the masked hypertension effect (MHE), and is not restricted to blood-pressure (BP) values around the thresholds for normal BP. We investigated the prevalence and persistence of MH and MHE in patients who were being treated for high BP and who had been followed for a period of 1 year. METHODS One hundred and sixty-one treated hypertensive patients underwent office blood-pressure measurements (OBPMs) at seven visits and self-performed blood-pressure measurements (SBPMs) for 1 week before each visit over a period of 1 year. All measurements were performed with the same type of automatic device. At each visit, MH was determined according to the European Society of Hypertension definition (OBPM, <140/90 mm Hg; SBPM, >/=135 mm Hg or 85 mm Hg). In addition, we determined prevalences of MHE at 5/3 mm Hg (SBPM exceeds OBPM by 5 mm Hg systolic and 3 mm Hg diastolic), and MHE at 10/6 mm Hg (SBPM exceeds OBPM by 10 mm Hg systolic and 6 mm Hg diastolic), respectively. RESULTS During the entire study, 50% of the patients had MH, and 40% had MHE at 5/3 mm Hg at least once. At four sequential OBPM visits, 2% consistently had MH, and 3% had MHE at 5/3 mm Hg or MHE at 10/6 mm Hg. The prevalence of MH increased with lower OBPM levels but remained rather constant for MHE at 5/3 mm Hg and MHE at 10/6 mm Hg. The persistence of MH and the MHE over time in individual patients was low. CONCLUSIONS We conclude that MH and MHE at 5/3 mm Hg and MHE at 10/6 mm Hg commonly occur in treated patients, but are not persistent phenomena and probably result from an accidentally low OBPM value on one particular occasion.