COMMENTARY

Measuring BP Is Simple, Right? Not so Fast

William C. Cushman, MD; Kenneth W. Lin, MD, MPH

Disclosures

August 14, 2018

Editorial Collaboration

Medscape &

William C. Cushman, MD: Hello. I am Bill Cushman. I am at the Veterans Affairs (VA) Medical Center at the University of Tennessee Health Science Center in Memphis, Tennessee.

Kenneth W. Lin, MD, MPH: Hi. I am Kenny Lin. I am a family physician at Georgetown University Medical Center in Washington, DC.

Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC 7 and JNC8)

Cushman: Welcome. I'm going to start out by giving a brief overview of the last several major US hypertension guidelines, and particularly the most recent 2017 American College of Cardiology (ACC)/ American Heart Association (AHA) guidelines,[1] which were published in November 2017. The seventh Joint National Committee on Prevention, Detection, Evaluation, and Treatment (JNC 7) came out in 2003.[2] It was actually a fairly comprehensive guideline, covering many different aspects of hypertension, classification, management, care, use of drugs, and blood pressure (BP) goals.

In 2014, the eighth Joint National Committee (JNC 8) report[3] was published. It was not intended to be a comprehensive guideline and, therefore, anything that had not been changed since JNC 7 would still be pertinent or relevant. JNC 8 focused on three major things: whom to treat for hypertension; BP targets; and medications. JNC 8 did not attempt to discuss classification; it gave just a minor statement about BP measurement.

I was on JNC 7 and JNC 8. I was not on the most recent ACC/AHA guidelines committee. I was an official reviewer for those guidelines so I am fairly familiar with them. They were intended to be a comprehensive guideline and to replace JNC 7 and JNC 8 as the next major US hypertension guideline.

ACC/AHA 2017 Guideline for High Blood Pressure in Adults

Cushman: The ACC/AHA guidelines go into a lot more detail, particularly about BP measurement. One thing that is different in the ACC/AHA 2017 guidelines is the BP classification for hypertension, with a lower definition of 130/80 rather than 140/90.

It also gives different goals for BP, and a lot of that is based on the fact that, in the interim between JNC 8 and the 2017 guidelines, the SPRINT trial[4] was published. That certainly led to some differences in BP goals.

What we want to focus on today is BP measurement issues. More than any prior guideline, the ACC/AHA guideline goes into great detail on how we should properly measure BP in the clinic and out of the office.

Patients with white coat hypertension have never been excluded from randomized controlled trials showing the benefit of treatment...partly because we didn't know who they were.

The guideline acknowledges that in most clinical settings, BPs are not being measured according to the standards that we used in various clinical trials. That is important because measuring BP incorrectly, even though there may be seemingly minor differences in how we are measuring it, can lead to tremendous error in results, usually with an overestimation of BP.

In-office measurement. The ACC/AHA guideline goes into a great deal of detail in terms of how we should measure clinic BPs. A few essential things are the use of the proper cuff size and a valid manometer. In addition, the patient should sit in a chair with their back supported and rest—not talk nor be spoken to—for 5 minutes before the readings, and then multiple readings should be taken. There are other aspects to it, but you can find in the guidelines a great deal of detail to this. In theory, it is really not that difficult to do. The difficulty is setting up the clinic so that you can have patients sitting alone and resting for that period of time.

Out-of-office measurement. Even though prior guidelines talked about out-of-office BPs, a lot more information is available, and the ACC/AHA guidelines put a lot of emphasis on the use of out-of-office BP for the diagnosis and management of hypertension. What we don't have is a trial showing whether there is a difference in outcomes between using out-of-office BPs versus office BPs. Epidemiologic data show that out-of-office BPs correlate better with events than clinic BPs do,[5] but we don't know whether using those out-of-office BPs primarily to identify whom to treat and how to treat, and what goals to treat to, will make a difference in outcomes.

The guidelines emphasize the use of out-of-office BPs similarly to the US Preventive Services Task Force.[6] First of all, before diagnosing somebody with hypertension who has elevated clinic BPs, particularly if not that elevated, the BP should be confirmed as elevated either with ambulatory BP monitoring or with home BP monitoring.

Distinguishing White Coat Hypertension

Cushman: A lot of epidemiologic data suggest that those who have elevated office BPs and normal home BPs—so-called "white coat hypertension"—may not be at very high risk and therefore may not need treatment. One difficulty with this is that recent studies, including a Spanish study that was published recently in the New England Journal of Medicine,[7] suggest that white coat hypertension actually is associated with long-term elevated risk.

Patients with white coat hypertension have never been excluded from randomized controlled trials showing the benefit of treatment. That is partly because we didn't know who they were. If we'd known who they were, perhaps we would have seen that they did not benefit within the period of the trial. But we don't know that at this point, so there is a little bit of uncertainty.

Distinguishing Masked Hypertension

Cushman: The other reason that the guideline recommends doing out-of-office BPs is to identify masked hypertension. Studies vary [but this may affect as many as] 10%-20% of people with hypertension. Masked hypertension is when an individual has normal clinic BPs but elevated BP either on ambulatory BP monitoring or home BP monitoring. This has been identified as an important group because epidemiology suggests that those individuals are at high risk.[8] Sometimes they are [at the same or] even higher risk than people with elevations in office and home BP. Therefore, the guidelines recommend identifying these individuals. They are usually patients who have BPs in the upper range of normal or elevated range according to the new guidelines. Yet, when using home BPs or ambulatory BP monitoring, they are found to have high BPs at home.

One of the difficulties is that we have never known who these people are when we have done clinical trials, and we never entered them into clinical trials. We don't have Grade A evidence that treating these individuals would reduce morbidity and mortality. I think there is going to be a lot more discussion about this, and I know Dr Lin has some perspective and some comments on this as well.

I would come back to the fact that we need to start with proper measurement of BP in the clinic, and there are good videos in addition to the description in the guidelines for how to do that.

Challenges of New Guidelines in Primary Care

Lin: Dr Cushman did a terrific job summarizing the guidelines for BP measurement and the evidence basis behind them.

One of the concerns in the primary care community about the new guidelines, and particularly the lower definition of BP and lower thresholds for BP treatment, is that often we are not measuring BP in appropriate ways in primary care offices. If we implement the guidelines without implementing the measurement portions, we may end up overtreating patients who don't truly have high BP.

Electronic health records...do not have an easy way to enter several [BP] measurements.

For example, I'm thinking about the last time I went to see my own primary care physician and had my BP measured. I was chatting with the medical assistant as she was taking my BP; they checked it one time. I don't recall them doing it again, and I think this is fairly common practice.

Implementing the appropriate BP measurement requires a lot of retraining both in terms of the BP measurement technique and the nurses or medical assistants who are taking the BP, as well as with data input. Electronic health records often only have one blank to record the BP that was taken. They do not have an easy way to enter several measurements and a way to show an average of those measurements.

Dr Cushman also mentioned the out-of-office BP emphasis in the guidelines. Indeed, the US Preventive Services Task Force in 2015[6] initially recommended that all BPs be confirmed with ambulatory BP monitoring. Their final recommendations did not include that recommendation because there was a lot of pushback. Many physicians didn't have access to it or insurance does not cover it for many patients.

I think ambulatory BP monitoring is considered to be the gold standard, but if you are not near a place where it can be done, or you don't have the capabilities in your office to provide it, it is often difficult. I am fortunate enough to be at an academic medical center where I can refer patients to have this done, but even so, often they are told that their insurance may not cover it. It's a $250 charge if it isn't covered, which for some patients is a big obstacle, particularly if they are not terribly motivated to have their BP measured in the first place. Other issues with patients may be that they are not accepting that the BP might be elevated or they are not taking prescriptions that are prescribed for their BP.

Home Blood Pressure Monitoring

Lin: The concerns with home blood pressure monitoring are probably more on the physician's side. Primary care physicians may be concerned that patients won't use appropriate techniques. They may run into circumstances where patients did home monitoring but didn't bring in the log of readings, so they have no idea what the readings were. If this goes on for a while, it may postpone treatment of people who do have elevated BPs, but for whom you are unable to get that kind of verification. I think those are the main problems that we see in primary care for translating the evidence into practice.

Cushman: I was also in a recent National Heart, Lung, and Blood Institute workshop looking at BP measurement, and we think that there really does need to be a change in how we typically measure BP in clinic settings. One of the ways to facilitate that is to get fully automated oscillometric manometers that are valid. What I mean by that is not only an automated manometer, but one that can be set to wait the 5 minutes and then take multiple readings. In my clinic setting, I enter the average BP into the medical record so that other people are not wondering what BP I am going to use. Just as you described when you were seen recently, I think the problem with the way it is often done is how much that error or variation is unpredictable from patient to patient. Even within the same patient, BP may be very different from visit to visit if it's not done correctly.

The only way to overcome that is to really do it correctly. We need to promote a culture change as much as possible. We have some evidence that you can do BP readings in the waiting room as long as nobody is interacting with the patient and you have automated machines that wait the 5 minutes before taking the readings. Certainly, those are some important changes that can and hopefully will begin to take place in practice.

Lin: That is a great suggestion. We already have automated check-in, and often patients get patient education at a terminal when they are sitting and waiting for their BP to be taken.

Cushman: I agree with what you said for home BP readings. There are a lot of difficulties with it and I cannot always trust that the readings were done correctly at home or reported correctly. Some machines, that do cost more, will automatically download the readings to a cell phone that can be sent to the physician. It's nice to have something that is automatically done.

There are now really good videos instructing patients on how to properly take home BPs. [Editor's note: Please refer to list of resources below.] The same errors that can be made in the office can be made at home as well. One was done by the VA recently, and another one was done by the American Heart Association and American Medical Association. These can be quite helpful.

Lin: I would like to thank everyone for joining us today in this discussion. I hope that it helps you with implementing the BP measurement guidance in the care of your patients, whether it's in the primary care setting or in cardiology practice.

Resources

New VA/DoD Video on Home Self-Measured Blood Pressure Monitoring

Million Hearts Campaign

CDC Guidelines for Self-Monitoring

New AHA/AMA Video on Home Self-Measured Blood Pressure Monitoring

ACC CardioSmart: How to Take Your Blood Pressure at Home

ACC CardioSmart: Blood Pressure: Know Your Numbers

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