Prognostic significance of the white coat effect

The difference between clinic and ambulatory blood pressure (BP) has been used to quantify the pressure reactivity to the doctor's visit (white coat effect). We investigated the prognostic significance of the clinic-ambulatory BP difference in the setting of the Progetto Ipertensione Umbria Monitoraggio Ambulatoriale (PIUMA) study. A total of 1522 subjects contributed 6371 person-years of observation. All subjects had an initial off-therapy diagnostic workup including 24-hour noninvasive ambulatory BP monitoring. The predicted values of ambulatory BP progressively diverged from the identity line (white coat effect of 0 mm Hg) with increasing clinic BP, but the predicted values of clinic BP tended toward the identity line with increasing ambulatory BP. Hence, the clinic-ambulatory BP difference showed a direct association with clinic BP and an inverse association with ambulatory BP. Consequently, a high clinic-ambulatory BP difference predicted both a high clinic and a low ambulatory BP, whereas a low clinic-ambulatory BP difference predicted both a low clinic and a high ambulatory BP. The clinic-ambulatory BP difference showed also a direct association with age. During up to 9 years of follow-up (mean, 4.2 years), there were 157 major cardiovascular morbid events (125 nonfatal and 32 fatal). The rate of total cardiovascular morbid events did not differ (log-rank test) among the four quartiles of the distribution of the clinic-ambulatory BP difference (2.13, 2.92, 2.10, and 2.83 events per 100 patient-years for systolic BP and 2.94, 2.14, 2.58, and 2.16 events per 100 patient-years for diastolic BP). Also, the rate of fatal cardiovascular events did not differ among the four quartiles of the distribution of the clinic-ambulatory BP difference. The clinic-ambulatory BP difference, taken as a measure of the white coat effect, does not predict cardiovascular morbidity and mortality in subjects with essential hypertension.