Editorials

How should we take blood pressure in clinical practice?

The wider use of home and ambulatory monitoring should be encouraged

Papers BMJUSA p 549

From BMJ USA 2002;October:541

It is increasingly clear that the traditional way of measuring blood pressure in the clinic or office frequently produces numbers that grossly overestimate a patient's true blood pressure level. This is a major problem, since it is one of the most important and frequent measurements made by physicians. Two major trends have brought this issue to the forefront: first, the development of new technologies for measuring blood pressure; and second, the increasing body of evidence that even mild elevations of blood pressure are associated with increased cardiovascular risk.

The traditional gold standard for evaluating blood pressure has been clinic readings made by a physician using a mercury sphygmomanometer. It is hallowed by time, and also by the fact that it has been the standard method for evaluating the risks associated with high blood pressure and the benefits of treating it. It has been known for more than 50 years that the blood pressures recorded in the clinic are substantially higher than readings taken by the patient at home,¹ but this fact was largely ignored until the advent of ambulatory blood pressure monitoring (ABPM). In the past 20 years a series of publications have shown that cardiovascular risk is predicted better by ambulatory blood pressure than clinic pressure.²

This is not surprising, since it is generally assumed that it is not the blood pressure recorded at a single point in time that causes damage, so much as the average blood pressure. The main finding has been that patients with "white coat" hypertension, who constitute approximately 20% of the population with mild hypertension,³ are at relatively low risk in comparison with patients whose blood pressure is persistently elevated. Furthermore, the white coat effect, which is usually defined as the difference between the clinic and daytime ambulatory blood pressure, is present in the majority of hypertensive patients. While these facts have generally been accepted in the research community, they have not yet exerted much influence on everyday clinical practice.

Two recent studies by Little et al, one reprinted in this issue (p 549), confirm that the white coat effect is of substantial magnitude (19/11 mm Hg) in the primary care setting⁴ and that self-measurement of blood pressure at home is the method preferred by patients, giving a much smaller white coat effect (5/6 mm Hg).⁵ The authors concluded, "It is time to stop using high blood pressure readings documented by general practitioners to make decisions about treatment."⁴ This is a sweeping statement, and one that will be resisted by many physicians who instinctively believe that the readings that they take in the traditional way are inherently more trustworthy than ones taken with an electronic gadget.

However, the hard truth is that whenever physicians' readings are compared with home and ambulatory readings, it is the physicians' readings that are the odd man out.⁶ Given that their measurements tend to consistently overestimate a patient's prevailing blood pressure level, some additional method is clearly needed. One solution would be to advocate the widespread use of ABPM, but there are other possibilities. The most obvious is self-monitoring, which is relatively cheap and convenient and less burdensome for patients than ABPM.⁷ Like ABPM, it can provide large numbers of readings and minimize the white coat effect (to allow for this, the "normal" limit of home blood pressure should be 135/85 mm Hg). So far, only one study has shown that home monitoring gives a better prediction of risk than clinic pressure,⁸ but it is particularly useful for monitoring the response to treatment and gives better correlation with the regression of left ventricular hypertrophy than does clinic pressure.

A practical regimen for patients who present with high clinic pressures and in whom treatment decisions are unclear is as follows: If there is evidence of blood pressure-related target organ damage, treatment is indicated. If such evidence is not present, home readings may be helpful to confirm an elevation. If these are high (above 135/85 mm Hg), treatment is indicated. If they are normal and if there is a persistent discrepancy between clinic and home readings, ABPM may be useful to make the final decision.

These considerations are not intended to mean that physicians should throw away their sphygmomanometers, but they should come to accept that they do not have a monopoly on accurate blood pressure measurement. Patients should be encouraged to monitor their own blood pressure regularly, and their monitors should be checked for accuracy. In circumstances where small differences of blood pressure may alter treatment decisions, more is better, and supplementing physician measurements with readings taken out of the office will improve patient care.

Thomas G Pickering, professor of medicine. 

Marie-Josée and Henry R Kravis Center for Cardiovascular Health, Mount Sinai School of Medicine, New York, NY 10029-6574 Thomas.pickering{at}msnyuhealth.org

Footnotes

Competing interests: Dr. Pickering is a consultant for Lifeclinic.com, a subsidiary of Spacelabs, Inc.