White coat hypertension: time for action.

Although increased blood pressure is one of the most powerful predictors of cardiovascular morbidity, the prediction for the individual patient is relatively weak. One reason for this is the inherent variability of blood pressure and the distortions associated with clinic measurement. It is widely accepted that blood pressure measured in the clinic commonly overestimates pressure measured in nonmedical settings and that the discrepancy between the 2 varies greatly from 1 individual to another. On the grounds that it is the average level of blood pressure to which the circulation is exposed over prolonged periods of time that causes the adverse effects of hypertension, rather than the pressure at any 1 moment, such as during a clinic visit, it is logical to suppose that ambulatory blood pressure will give a better prediction of risk than clinic pressure. A subgroup of patients with mild hypertension whose blood pressure is high only in medical settings has been identified as having white coat hypertension; this group typically comprises '20% of the hypertensive population. This is a potentially useful concept because it may help to define a group of patients who are at relatively low risk of cardiovascular morbidity and hence do not merit antihypertensive drug treatment. However, the definition of white coat hypertension is arbitrary and depends both on the cutoff point chosen to define a hypertensive clinic pressure and a normal ambulatory pressure.