Accurate Measurement of Blood Pressure: The Importance of Out-of-Office Monitoring

The accurate measurement of blood pressure (BP) remains the most important technique for evaluating hypertension and its consequences, and there is increasing evidence that the traditional office BP measurement procedure may yield inadequate or misleading estimates of a patient's true BP status. The limitations of office BP measurement arise from a number of sources:

1. the inherent variability of BP coupled with the small number of readings that are typically taken in the doctor's office
2. poor technique (e.g. terminal digit preference, rapid cuff deflation, improper cuff and bladder size)
3. the white coat effect (the increase of BP that occurs in the medical care environment), and
4. the masked effect (a decrease of BP that occurs in the medical care environment that may lead to under-treatment; in the case of ‘masked' hypertension, the out-of-office BP is hypertensive while the resting, in-office BP is normotensive or substantially lower than the out-of-office BP).

Nearly 7 decades ago there were observations made that office BP can vary by as much as 25 mmHg between visits. The solution to this dilemma is potentially two-fold: by improving the office BP technique (e.g. using accurate validated automated monitors that can take multiple readings), and by using out-of-office monitoring to supplement the BP values taken in the clinical environment.

Out-of-office monitoring takes two forms at the present time: self (or home) and ambulatory BP monitoring. While both modalities have been available for 30 years, only now are they finding their way into routine clinical practice. The use of self-BP monitoring (also referred to as home BP monitoring) as an adjunct to office BP monitoring has been recommended by several national and international guidelines for the management of hypertension. In the USA and Europe, the use of self-BP monitoring is growing rapidly: Gallup polls suggest that the proportion of patients who report that they monitor their BP at home increased from 38% in 2000 to 55% in 2005. In contrast, the use of ambulatory BP monitoring (ABPM) in clinical practice remains limited, but exact numbers are not available.

Proceedings of a recent symposium by the European Society of Hypertension Working Group on Blood Pressure Monitoring have several valuable contributions that discuss the advantages of out-of-office BP measurement for predicting cardiovascular outcomes. These contributions are available on the website of Blood Pressure Monitoring.

William B. White, M.D., Professor and Editor-in-Chief Blood Pressure Monitoring.