White coat effect in treated versus untreated hypertensive individuals: a case-control study using ambulatory and home blood pressure monitoring

BACKGROUND: Some studies have shown a significant white coat effect (WCE) (i.e., difference between clinic blood pressure CBP and awake ambulatory blood pressure ABP) to be present not only in untreated but also in treated hypertensive individuals. This study aims to assess 1) the prevalence and the magnitude of the WCE in treated versus untreated hypertensive persons, and 2) the usefulness of home blood pressure (HBP) versus ABP in the detection of this phenomenon. METHODS: A case-control study was conducted in 138 treated hypertensive patients and same number of sex- and age-matched untreated hypertensive subjects who had measurements of CBP (at least three visits), HBP, and ABP. Subjects with a WCE of >20/10 mm Hg (systolic/diastolic) were classified as clinic reactors. RESULTS: There was a trend for a larger WCE assessed by ABP monitoring in the untreated group (mean difference in systolic WCE, 1.8 +/- 22.2 mm Hg, 95% CI -2.0 to 5.5; diastolic 1.8 +/- 11.9 mm Hg, 95% CI -0.2 to 3.8) and for more untreated clinic reactors (27% untreated v 20% treated, odds ratio 1.5, 95% CI 0.9 to 2.7). The sensitivity, specificity, and positive and negative predictive values of HBP to detect clinic reactors correctly were 56%/62% (treated/untreated), 87%/84%, 52%/59%, and 89%/86%, respectively, with moderate agreement between HBP and ABP (kappa 0.42/0.46). CONCLUSIONS: In treated hypertensive patients, WCE seems to be reduced compared with that in untreated hypertensive persons but is not eliminated. In both untreated and treated hypertensive individuals HBP monitoring appears to be useful in the detection of the WCE, but it may not be appropriate as an alternative to the ABP method.