New recommendations on blood pressure screening from the U.S. Preventive Services Task Force (USPSTF) suggest that prior to starting any treatment, elevated blood pressure readings taken in the doctor’s office should be confirmed by a number of similar readings from outside the clinic.
The recommendations appeared online in the Annals of Internal Medicine in late 2015.
High blood pressure is a major risk factor for heart attacks, strokes and chronic kidney disease, but it’s a symptomless disease, so the cuff is the only way to see it coming. Combine the diagnostic shortcomings of office-based blood pressure measurements with the fact that about a third of American adults have hypertension and these new recommendations could alter the care of millions.
It’s not that office BP measurements are so inaccurate, particularly now that most are performed with automated BP cuffs rather than with manual devices, which are more prone to human error. It’s just that they provide very few numbers, in an environment that is hardly routine.
Hard to Pin Down
Blood pressure is not a fixed number, like one’s height. It’s physiologic; it bounces up and down during the day, depending on the body’s demands. Stub your toe on the kitchen table and your blood pressure will go up — but that doesn’t mean you have hypertension.
Even Flo, the ubiquitous and ditzy spokesperson for Progressive Insurance, understands how important it is to acquire large amounts of real world data. If Flo wants to know what your real driving habits are, she won’t ask you to drive by the office a couple times so she can beam you with a radar gun. Instead, she’ll ask you to enter Progressive’s Snapshot program, which involves plugging a small device into the on-board diagnostic port of your car. For 30 days, or longer if you prefer, the device will record the time of day, speed, and G force (in some devices) for every second you drive.
At least 20 percent of patients who have elevated blood pressure readings in the clinic setting don’t have high blood pressure the rest of the day.
Ditzy Flo wants a lot of data points, but up until now, we physicians — the “do no harm” people — have been diagnosing patients as hypertensive (or not hypertensive) based on a relatively small scattering of office blood pressure readings. According to accepted hypertension guidelines, the number of measurements might be as low as four: two elevated blood pressures on two separate visits, and let the treatment begin.
Many Overtreated, Undertreated
How inferior are “unreal” office blood pressure readings in making the diagnosis of hypertension?
It turns out that at least 20 percent of patients who have elevated blood pressure readings in the clinic setting don’t really have high blood pressure the rest of the day. We call this “white coat hypertension.” These people don’t need medication but they’re either getting it or they’re explaining to their doctor why they don’t need it.
And 10 to15 percent of those who have normal blood pressure in the office are hypertensive the rest of the day. We call this “masked hypertension.” They should be on treatment but aren’t.
Put those percentages up against the estimated 70 million Americans who have hypertension, and even Flo can see those are big numbers. Too many people are falsely diagnosed with hypertension and too many are missed.
The point isn’t to delay and stonewall the treatment of those people who are truly hypertensive — repeatedly elevated office blood pressure values certainly do increase the likelihood that one is indeed hypertensive, as do risk factors such as obesity, being over age 40 or being African-American.
A Better System
How then to get the diagnosis right? With either a validated home blood pressure monitor or with a device called ambulatory blood pressure monitoring (ABPM). It’s a standard-looking automated blood pressure cuff except it includes a monitor to record the data. The cuff inflates every 20 to 30 minutes for a 24-hour period, whatever you do, wherever you go, and that includes sleep. The next day, you drop the device back off at the clinic and the data is downloaded.
The USPSTF recommends ambulatory blood pressure monitoring as the reference standard for confirming the diagnosis of hypertension. But it also says “good-quality evidence suggests that confirmation of hypertension with HBPM [home blood pressure monitoring] may be acceptable.”
The nod goes to ABPM over home monitoring for a couple of reasons. For most people, our blood pressure dips about 10 percent lower during sleep and stays there until around the time we wake up. But there are those who don’t dip, and these so-called ‘non-dippers’ seem to be at higher risk of hypertension-related problems like heart attacks and strokes. Home blood pressure monitors can’t follow you to bed…yet.
And while ABPM is automatic, the recommended home monitoring regimen is intentional and, well, regimented: two times in the morning and two times in the evening for a minimum of three consecutive days, but preferably seven consecutive days. Compare that to ABPM’s “one-and-done” approach.
And doctors will tell you that in patients with any obsessive-compulsive traits, a home blood pressure monitor can become a maniacal overlord. A few elevated numbers can send these people into an adrenaline-soaked tailspin that only drives their numbers higher. For the most part, physicians are interested in blood pressure trends rather than any single individual reading.
One advantage to home blood monitors is that they are now widely available, but ABPM has generally been available only in a small number of clinics, typically in a cardiology or kidney clinic. It’s also been expensive (several hundreds of dollars), and not well reimbursed — or not reimbursed at all — by insurance companies.
Taking Matters Into Their Own Hands
Frustrated by the knowledge of how much they were missing, two colleagues who are internists here in Minneapolis purchased several ambulatory blood pressure monitors and educated themselves and their clinic partners in how to interpret the data. They brought the cost of ABPM down to around $75, and they’ve been impressed at what ambulatory blood pressure monitoring has revealed about their patients’ true blood pressure.
It’s important to note that the “white coat” (falsely elevated) and “masked” (falsely low) effects also apply to patients who are already on treatment for correctly diagnosed hypertension. They may not need a second or third medication added to their regimen if their stubbornly elevated office blood pressures don’t hold up on ABPM. They may need more if office readings are falsely low.
A companion article to the new USPSTF recommendations in the Annals of Internal Medicine points out that we’ve had evidence of office blood pressures’ diagnostic inferiority and ambulatory blood pressure monitoring’s superiority for “several decades.”
These changes have been a long time coming. Sometimes the future takes a while to get here.
“Imagine that the term ‘cancer’ was substituted for ‘hypertension’ and one had a biomarker for the cancer that had a 20 percent false-positive rate. It is hard to believe that one would label all people with the abnormal biomarker as having cancer if simple further testing would clarify the diagnosis.”
-Thomas Giles, MD,The Journal of Clinical Hypertension
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