The phenomenon of white-coat hypertension—when a patient experiences high blood pressure in the office, but not outside of it—is now widely recognized by physicians and a catalyst for the push for measurements at home to ensure accuracy in BP measurement to inform hypertension diagnosis and treatment.
But there is another culprit lurking that threatens accurate measurement of blood pressure in the physician’s office.
Who is that masked person? It’s called masked hypertension, and it is just the opposite of white-coat hypertension. Masked hypertension, by contrast, is when someone doesn’t have high blood pressure in their doctor’s office, but it is high outside of the office.
It’s real, and it’s risky
Daichi Shimbo, MD, a preventive cardiologist in New York City, begins his summary on masked hypertension by noting the two forms of blood pressure measurement.
“Traditionally, we've measured blood pressure in the office, and we say you're either high or not high,” Dr. Shimbo said. “But we also have out-of-office blood pressure monitoring including home monitoring, which can be considered a measure of what I call true, or ecological, blood pressure (i.e. blood pressure in the real world outside of the office).”
Out-of-office measurement gets only a fraction of the emphasis of in-office measurement, and high out-of-office blood pressure can pose substantial risks to patients, he noted.
“If you go into your doctor's office and you're completely relaxed and they find your blood pressure is normal, but outside you're a FedEx driver and you lift heavy boxes all day and your blood pressure is always high, I would argue that's actually your blood pressure, because it's happening in the real world,” said Dr. Shimbo.
In fact, the only way to determine a patient’s real blood pressure is to measure both ways, he said, pointing out four scenarios:
- Not high in office, not high out of office: sustained normotension.
- High in office, not high out of office: white coat hypertension.
- Not high in office, high out of office: masked hypertension.
- High in office, high out of office: sustained hypertension.
The last two are arguably the most dangerous, Dr. Shimbo said, noting that the trick is distinguishing between masked hypertension and sustained normotension since the office blood pressure in both conditions are normal.
“It's called masked hypertension because it's hidden. If you don't do out-of-office monitoring, neither you nor the doctor will know you have hypertension,” he said. “It turns out that your risk of cardiovascular disease events is about 1.7 times higher if you have masked hypertension compared with sustained normotension.”
Dive deeper:
- Top answers to patients' questions about normal blood pressure
- Validated devices: The missing link in state Medicaid BP efforts
- Why a validated device listing is important for BP control
So then, who to monitor?
One of the challenges facing care teams is deciding who to monitor for masked hypertension.
If physicians or other health professionals in the health care system were to attempt out-of-office monitoring on everyone without high office blood pressure, for example under 130/80 mm Hg, then that would be a lot of people to screen—more than 120 million US adults. This is hardly feasible.
What doctors wish patients knew
Subscribe for the answers to the latest questions patients are bringing to the exam room.
“However, we know from past studies that people who have office blood pressure levels close to the high blood pressure threshold but not over it, have a high prevalence of masked hypertension,” said Dr. Shimbo, noting that the 2017 American College of Cardiology and American Heart Association BP guideline recommends performing out-of-office monitoring to screen for masked hypertension for those who have office readings of 120 to 129 mm Hg or 75- or 79-mm Hg. Using this approach, about 41 million U.S. adults would need to be screened—this is more manageable.
How to do out-of-office BP
There are two main forms of out-of-office blood pressure monitoring: ambulatory blood pressure monitoring and self-measured blood pressure (SMBP) monitoring at home. Ambulatory blood pressure monitoring requires a patient to wear a device that takes a blood pressure reading every 15 minutes for over a single 24-hour period. SMBP, also known as home blood pressure monitoring, involves a patient taking two blood pressure measurements one minute apart, twice daily for seven days.
Setting aside the arguments over which may be more accurate—it’s something Dr. Shimbo said hasn’t been resolved—SMBP is far more accessible.
“In the U.S., a primary care doctor does not typically do ambulatory blood pressure monitoring,” he said. “A patient has to go to a specialized hypertension center for that.”
So, for the majority of primary care physicians, SMBP monitoring is the only option for monitoring patients for masked hypertension. To do it right, however, a patient needs an accurate measurement device.
“Anyone can go to Rite Aid or Duane Reade or Amazon and buy a home device that is cleared by the” Food and Drug Administration (FDA) "to be sold, but it might not be accurate,” Dr. Shimbo said, noting this often-confusing distinction between FDA clearance and what hypertension experts think is accurate. “A lot of patients and physicians don't know that.”
To fix this problem, the AMA helped create the US Blood Pressure Validated Device Listing (VDL™), which identifies the BP measurement devices that have been independently validated for accuracy. The list now contains 65 validated home devices in a variety of price ranges. Validated cuff sizes are noted for each device.
“It's not funded by industry,” Dr. Shimbo said. “It’s scientists and clinicians reviewing the data and saying This is what we think has have surpassed the bar for accuracy.”
In addition, the AMA has developed the 7-Step SMBP Quick Guide to show care teams how to use telemedicine modalities with self-measured blood pressure to help patients with hypertension achieve and maintain blood pressure goals.
Getting back to the better diagnosis of hypertension, Dr. Shimbo said there is a lot of data suggesting that masked hypertension’s risks are similar to those of sustained hypertension.
“So, getting it right is important,” he said. “That's my pitch for masked hypertension: It’s a real entity that has consistently been shown to be associated with increased cardiovascular disease events. Unfortunately, a lot of people don't know about it.”
AMA MAP™ Hypertension is an evidence-based quality improvement program that provides a clear path to significant, sustained improvements in BP control. With the AMA MAP program, health care organizations can increase BP-control rates quickly. The program has demonstrated a 10% increase in BP control in six months with sustained results at one year.
