A Study of the White-Coat Phenomenon in Patients with Primary Hypertension

The objective of this study was to evaluate whether the discrepancy between clinic and home blood pressure (BP) in hypertensive subjects would disappear or diminish in magnitude if the BP measurement was taken under controlled conditions differing only with respect to location (clinic vs. home). Three hundred and sixty-seven patients aged 34-84 years with primary hypertension were enrolled. All of the patients or their spouses were taught to measure BP correctly with their own sphygmomanometer at home. The home BP value (HBP) was calculated as the average of 45 readings over 15 days. On days 6, 12, and 18 of the measurement period, rather than measuring their BP at home, patients and their spouses were asked to visit the hospital at the usual time of their BP measurement and to bring their own sphygmomanometer. The clinic BP value (CBP) was calculated as the average of the 9 readings taken on these visits by the patients or their spouses. The "white-coat phenomenon" (WCP) was considered to be present when the difference between the CBP and HBP was greater than 20/10 mmHg. The mean reading of home systolic/diastolic BP was 134.7/79.1 mmHg and the mean reading of clinic systolic/diastolic BP was 149.8/86.4 mmHg. In the total subject group, the prevalence rate of WCP was 31%-35% if the WCP was defined as DeltaBP (CBP - HBP) > or =20 mmHg/10 mmHg. In conclusion, ruling out the influence of different factors, including time of day, the sphygmomanometer, the individual taking the BP measurement, the climate, and the patients' health or mood, the WCP was still found to exist to a statistically significant degree. This study indicated that teaching patients to measure their own BP at home is an effective procedure to obtain a more accurate result of their BP level. It also helped to involve the patients more actively in controlling their hypertension.