Background: In large-scale surveys of individuals with hypertension those whose clinic blood pressure is reduced to 140/90 mmHg or less have been found to represent only a small fraction of the hypertensive population. We assessed whether these results arise because of a white-coat effect elevating clinic blood pressure. Methods: We randomly selected 2400 individuals from the town of Monza, Italy, and invited them to take part in our study. We measured clinic blood pressure as well as home (morning and evening measurements), and 24 h ambulatory blood pressure - ie, blood pressures largely devoid of a white-coat effect. Based on clinic blood pressure participants were then classified as normotensive, untreated hypertensive (clinic blood pressure > 140 mmHg systolic and/or > 90 mmHg diastolic), or treated hypertensive (having antihypertensive treatment). The mean blood pressures for each group were calculated. Findings: 1651 people took part in the study. The clinic blood pressure of treated hypertensives (n = 207; 146.9 [SD 18] mmHg/90.2 [8.6] mmHg) was only slightly less than in untreated hypertensives (n = 402; 148 [15.2] mmHg/93.3  mmHg) and in both groups the blood pressure values were much greater than those of normotensive individuals (n = 1042; 119.5 [10.3] mmHg/78.1 [6.6] mmHg) p <0.001. Averaged home and 24 h blood pressures were lower than clinic blood pressures but similarly higher in untreated and treated hypertensive individuals when compared with normotensive individuals. This was also the case for day, and night average blood pressures. The number of treated hypertensive patients found to have blood pressures within the normal limits was small not only when based on clinic blood pressure values but also when based on ambulatory blood-pressure values. Interpretation: In the hypertensive population the number of patients with inadequate blood-pressure control is high not only when assessed in the clinic but also when assessed by ambulatory-blood-pressure monitoring or at home. The high blood-pressure values commonly found in treated hypertensive individuals cannot be accounted for by a white-coat effect but by a true lack of daily-life blood-pressure control.
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