Survey of white coat hypertension

Editor—Muscholl et al reported that patients with white coat hypertension showed evidence of target organ damage as manifested by changes in left ventricular structure and function when compared with normotensive subjects.1 Though interesting, their results are misleading. The conventional method for identifying patients with white coat hypertension is by comparing blood pressure measured by a physician in a clinic with measurements made with 24 hour ambulatory monitors. Although there is no agreement as to the exact criteria, the central concept of white coat hypertension is that it is characterised by high blood pressure only in the medical setting; blood pressure is normal at other times. In Muscholl et al’s study, all the blood pressure measurements were made in a medical setting. After at least 30 minutes’ rest, blood pressure was measured three times by a technician, and the means of the second and third readings were used as the baseline or “non-physician” blood pressure. These readings were compared with blood pressure measured once by a physician after an echocardiographic examination. Patients were classified as having white coat hypertension when the blood pressure measured by the technician was <140/90 mm Hg and that recorded by the physician was ⩾160/95 mm Hg. The authors provide no evidence that the technicians’ readings are in any way representative of measurements in a non-medical setting, and previous work has shown that although blood pressure measured in a clinic by a non-physician (in this case a nurse) was substantially lower than the physician’s readings,3 it is not a reliable way of diagnosing white coat hypertension. The difference in the procedures used by the technician and the physician is also a problem. The technician measured blood pressure three times before the echocardiographic examination, with the first reading omitted from the analysis, whereas the physician measured it only once, after the echocardiographic examination. This makes meaningful comparison between the two sets of readings difficult. We do not accept the authors’ conclusion, based on their data, that white coat hypertension is not a benign condition, because their method of defining white coat hypertension is so different from other definitions in the medical literature.