White coat phenomenon in patients receiving antihypertensive therapy.

The occurrence of the white coat phenomenon in hypertensive patients receiving drug therapy was determined in a consecutive series of 71 patients undergoing ambulatory blood pressure (ABP) recordings because of suspected differences between office and ambulatory values. Overall mean (+/- SEM) office blood pressure (BP) was 166 +/- 2/95 +/- 1 v awake ABP 139 +/- 2/86 +/- 1 mm Hg. The white coat phenomenon [(office BP - ABP) greater than or equal to 20/10 mm Hg] was present in 52 of 71 patients: office BP 170 +/- 3/96 +/- 2 v ABP 135 +/- 2/83 +/- 1 mm Hg. A marked white coat effect [(office BP - ABP) greater than or equal to 40/20 mm Hg] was seen in 22 patients with office BP being 178 +/- 4/98 +/- 3 v ABP 131 +/- 3/79 +/- 2 mm Hg. The frequent occurrence of white coat phenomenon in these patients suggests that office BP readings may not always represent usual ABP in patients receiving chronic antihypertensive therapy.