Misclassification of Blood Pressure by Usual Measurement in Ambulatory Physician Practices

Standardized measurement of blood pressure (BP) is widely recommended but rarely followed in usual clinical practice. We compared the classification of hypertension status of 107 patients referred by family physicians for ambulatory BP monitoring (ABPM) and with elevated clinic BP when assessed by usual clinical office measurement, a trained hypertension research nurse using a standardized measurement protocol, or an ambulatory BP monitor. Usual clinic readings resulted in higher BP readings than those obtained by the research nurse: mean (95% confidence interval [CI]), 10.8 (8.0 to 13.6)/4.9 (2.9 to 6.9) mm Hg, the daytime ambulatory BP 7.7 (5.1 to 10.3)/5.1 (3.0 to 7.1), and the 24-h ambulatory BP 12.1 (9.6 to 14.6)/8.9 (6.9 to 10.9). The interpretation of whether the patient had a hypertensive versus normotensive reading in the usual clinic setting differed in 42% of patients relative to standardized nurse readings. Following standardized technique is important for correct classification of the BP status of patients. Use of usual or casual technique results in higher readings than standardized or ambulatory BP readings. This study indicates that significant improvement in the assessment of BP is required for diagnosis and optimal management of hypertension. Consideration strongly needs to be given to the development of alternative methods of assessing BP in clinical practice.