Measuring BP at Home: The Key Readings

Henry R. Black, MD


July 29, 2011

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Hi. I'm Dr. Henry Black. I'm a Clinical Professor of Internal Medicine at the New York University School of Medicine, a member of the Center for the Prevention of Cardiovascular Disease at that institution, and immediate Past President of the American Society of Hypertension.

In my opinion, the year 2011 is going to be very important to the management of hypertension. It's becoming clear to everyone that hypertension has been somewhat of a neglected risk factor. We've been focusing a lot on cholesterol and on diabetes but, in fact, in all the epidemiologic surveys that have ever been done, hypertension has been the most important predictor of cardiovascular and kidney disease outcomes. This is not to ignore the others, but I think hypertension has been somewhat overlooked.

The reason 2011 is important is that the Eighth Joint National Committee for the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, or JNC8, should be coming out with its initial report by the end of this year, and the National Institute of Clinical Excellence (NICE), which is the British hypertension group, will be publishing their updated guidelines in August of this year. We expect some important changes.

Today I want to focus on where we measure blood pressure and how we do it. We've been measuring blood pressure in the office with pretty good quality control since really the 1930s. The "Build and Blood Pressure" study done by the insurance industry looked at office readings only. Sometimes people may have come to the home to measure blood pressure, but for the most part it was office readings. That study codified the idea that 140/90 mm Hg in the office was an elevated blood pressure. We've been tinkering with that over the years. We've staged it in the United States. They grade it in Europe. We've added different recommendations, but it has all still been based for the most part on a number, and that's a number from the office.

For the past 20 years, however, it has become more and more clear that there are other places to measure blood pressure. One of the important new areas is home blood pressure monitoring. We now have several inexpensive, easy-to-use machines that we can use at home and that give us readings we can follow serially over time. It has become clear from studies in Italy and elsewhere that home blood pressure is a very good predictor of outcomes. It wouldn't do any good if you were simply measuring blood pressure unless you had some outcome data as well.

The Finn-HOME study,[1] which was conducted in Finland from about 2001 to the end of 2009, included more than 2000 adults between ages 45 and 74 years and began to look at how many blood pressure readings you need to take and when you need to take them in order to predict outcomes. This is a seminal idea because one of the concerns that I used to have about home monitoring was that I was creating more blood pressure neurotics than I was actually helping. I tell my patients to take their blood pressures by a protocol, usually twice a day, sitting, after a little bit of rest, write them down, and then bring them in to me and we will go over what they've found. What I have, and I think many of my colleagues who do this have, is a long sheet of blood pressures. You don't really know what to do with them or which ones are important.

This is what the Finn-HOME study looked at. They evaluated the impact of taking 2 blood pressure readings twice a day for 1 week, for a total of 28 measurements. They looked at whether throwing out the first reading mattered, as some studies have indicated. They looked at whether you learned enough from 7 days, whether you only needed to do 3 days, or whether you needed to do more. They looked at whether it was systolic or diastolic blood pressure that was more important. Their findings are quite interesting. Whether you include the first reading of the day or not, those 28 readings seemed to provide an excellent prediction of outcomes, and you don't need more. The curve of prediction flattens out after about 3 days, and you might even get away with doing only 3 days' worth of measurements. But these authors ended up recommending 7 days.

When we're talking to a patient, a colleague, or a relative about whether they should take blood pressure readings at home, a couple of things are important to remember. First, make sure the instrument is validated, one that has been shown to be accurate. I'm not a fan of the wrist or finger press, but there are some people who are. These instruments need to be approved by the various societies that do this.

Second, using a protocol is key. You don't want people to take their blood pressures only when they think they are sick or only when they think they are well, only on weekends or never on weekends, for example. You want to get an idea of their real home monitoring measurements. According to this study, it looks as if taking 2 readings in the morning and 2 readings in the evening for a week, keeping the records, and bringing them in to the doctor will tell you all you need to know. The other value of this is that it reveals people with what we now call masked hypertension, whose blood pressures don't seem to be elevated in the office but turn out to be elevated according to home readings.

Whether or not home blood pressure monitoring will be as good as 24-hour ambulatory monitoring still remains to be seen, but it is simpler and less expensive. The Finn-HOME study plus earlier Japanese studies focus on [useful protocols]. Two blood pressure readings twice a day for a week should give us all we need to know about ultimate outcomes, according to the Finn-HOME study.

Thank you very much.