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Feature Article

The ups and downs of blood pressure measurement

You've just been to the doctor and your blood pressure is a bit high.

Or is it?

A recent study at the Durham VA Medical Center and Duke University confirms that people's blood pressure tends to be higher at the doctor's office than when they check it themselves at home.

The difference can often be as much as 10 or 15 points in the systolic, or top, number. So if your reading at the doctor's office is hypertensive—say, 140 over 90—it could well be only pre-hypertensive at home—130 over 85, for example. That's a bigger spread than the five-point gap between home and clinic that clinical guidelines recognize and advise doctors to account for in their decision-making.

But that's only part of the story. The VA-Duke study also suggests that regardless of where blood pressure is taken, the best way to get an accurate reading—to know a patient's "true" pressure—is to take at least five or six measurements on different days and use the average.

According to lead author Benjamin Powers, MD, MHS, an internist with VA and Duke, the only realistic way to get multiple measurements is to rely on home monitoring.

"Practically speaking, we can't bring people into the clinic more frequently to do this, and taking blood pressure five times during a single clinic visit is not going to accomplish the same thing."

Study compared readings across different settings

The VA-Duke hypertension study involved several hundred Veterans. It was mainly intended to test the effects of home blood pressure monitoring and phone calls from nurses that aimed to help patients improve behaviors such as diet, exercise, and prescription adherence.

The newest phase of the analysis, published in the June 21 Annals of Internal Medicine, zeroed in on the ideal way to measure blood pressure. How can providers get the most accurate information on which to base treatment decisions? The study compared results obtained through three methods: clinic measurements, home monitoring, and measurements by research assistants as part of a carefully controlled study protocol.

An editorial that accompanied the VA-Duke article, by a group with Johns Hopkins University, painted a disturbing picture of how hypertension treatment decisions are commonly made for U.S. adults. Aside from "white coat syndrome"—most patients' pressure spikes higher at the doctor's office, usually because they are nervous about their appointment—there is a fair degree of variation, and sloppiness, in how clinic readings are typically taken.

"In practice, blood pressure measurement is remarkably casual," wrote the Hopkins team. "As clinicians and patients, we have personally observed major deviations from accepted standards: Cuffs are applied over clothing, [blood pressures] are obtained without allowing the patient to rest for 5 minutes, and measurements are taken while the patient sits hunched over an examination table with his or her legs dangling. Training is minimal, and monitoring to check technique is nonexistent. Devices, even if initially validated, are not checked and, if needed, recalibrated."

Citing several studies that back their conclusion, the Hopkins authors say the result is that "suboptimal measurement of [blood pressure] is remarkably commonplace."

Powers concurs: "When people have looked at how well providers follow protocol in routine practice, it's usually pretty disappointing. Even small differences in the patient's arm position can make a difference of a few millimeters of mercury."

Many patients could be misdiagnosed as hypertensive

In the VA-Duke study, only one in three patients was consistently classified across all three methods used in the study. Based on home measurements, for example, about half the patients were found to have well-controlled pressure. Based on clinic measurements, the figure dropped to below one-third.

If such a trend were taking place at medical practices across America—as it likely is—millions of patients could be on hypertension drugs they don't really need.

Powers, an assistant professor of medicine at Duke, uses the analogy of diabetes. "What if you had to make your treatment decision for your patient with diabetes based on one random blood sugar measurement that you got in the clinic, and based only on that, you had to determine how to change their medication?"

He points out that hypertension is even more common than diabetes, and that the scope of the problem is potentially huge. "This occurs all the time," he says. "High blood pressure is the most common reason older adults visit the doctor. We've been able to measure blood pressure for a long time and treat it, and some of the things covered in our article are fairly well-known, but I don't know that on a regular basis we as clinicians in the U.S. are very mindful of the inherent error in measurement and the inherent variability in blood pressure, and how that impacts clinical decision-making."

VA in good position to tackle problem

VA, says Powers, is uniquely positioned to tackle the problem. With its shift to a model of primary care known as patient-aligned care teams (PACT), the agency will increasingly rely on home-based self-monitoring for hypertension and other chronic conditions. Telehealth staples such as phone follow-up and secure email and Internet contact will play a bigger role. The goal is to improve access and continuity of care, especially for those who live in rural areas or otherwise can't travel to VA care sites.

Powers has already figured out how to make good use of home monitoring with his hypertension patients.

"I get them a monitor that's validated, that fits, that works for them. I ask them to get me some info on their home blood pressure. Those who are Internet-savvy can send me a secure message through myHealtheVet. Others write it down and bring it to me at the clinic visit. So even though I might be seeing them in the clinic, I'm still making a decision based on their home measurements—ideally, several of them."

He notes that through VA's electronic medical record system, multiple blood pressure readings could be easily tracked and combined for patients.

Also, unlike the private sector, VA is free to use telehealth wherever and whenever it makes the most sense for patients.

"It's been difficult for private primary care providers to do because we're still working out how to pay private fee-for-service doctors for care that doesn't involve face to face interactions with patients," says Powers. "We are free from that constraint in VA, and we can provide the highest quality, most efficient care possible without having to rely on seeing people face to face in order to get paid."

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