For decades, doctors have been aware of a phenomenon known as “white coat hypertension” — when a patient gets higher blood pressure readings at the doctor’s office than they do at home, perhaps because they’re anxious in the clinic — but previous studies have shown inconsistencies in its effects.
Now, a large new meta-analysis confirms patients with the condition are more than twice as likely to die from a cardiac event as those whose blood pressure readings are always normal.
These same patients have a 33% increased mortality risk and are 36% more likely to experience a cardiac event like a heart attack, according to the study published Monday in Annals of Internal Medicine.
The analysis, which pulled data from 27 studies of the condition, paints a far clearer picture of the issue than earlier, single studies did, its authors noted. The findings are also particularly important for public health efforts to address heart disease and stroke, since hypertension is a known risk factor for those events but has no known symptoms. They point, too, to the importance of accurate blood pressure monitoring that patients can take on their own, some researchers argued.
“We were very interested in just clarifying the actual risk of isolated office high blood pressure with a normal blood pressure at home,” said Dr. Jordana Cohen, the paper’s first author and an assistant professor at the University of Pennsylvania Perelman School of Medicine. “It pulls the results together to give us, sort of, a stronger sense of truly what the signal is.”
The study also distinguished between two types of patients who had abnormal blood pressure readings in the doctor’s office — some received medications to bring down their blood pressure and some did not. Those who did get medication had no increased risk for cardiovascular events or death compared to those with normal blood pressure.
Cohen said the two findings together should encourage doctors to more closely monitor patients who show white coat hypertension if they aren’t getting medication — but also that they could be overtreating people with similar readings if they receive antihypertensive medication.
“In most situations, [patients who get medication] may be more prone to side effects from the blood pressure medications or to having low blood pressure as a result of their blood pressure medications,” Cohen said.
That finding calls into question the proper treatment for white coat hypertension, she said, suggesting the importance of further studies to examine what kind of interventions might be best.
“We’re not sure if treating it with the blood pressure medication helps,” she said. “You don’t want to cause them to have low blood pressures outside of the office, since normally, their blood pressure is normal outside of the office. But we don’t know what to do about it.”
Before this meta-analysis, many previous studies didn’t distinguish between patients with these results who got medication and those who did not, according to Cohen.
The study also divided patients into further subgroups. Cohen and her colleagues found that there was also an elevated risk of cardiovascular events or mortality when the patients in the study were older, when the duration of the study was five years or longer, and when ambulatory blood pressure monitoring systems were used as opposed to home blood pressure monitoring systems, compared to patients whose blood pressure readings were always normal.
Several researchers who weren’t involved in the new paper cautioned that meta-analyses like this one often consider too many variables. Dr. Stanley Franklin, a retired University of California, Irvine, professor who has published numerous studies on white coat hypertension, also pointed out that while some of the included studies may have performed valid, robust analyses, others may not have — compromising the integrity of the meta-analysis as a whole.
Cohen argued that while that may be true in some cases, the inconsistency in the data available to them was exactly why a meta-analysis was necessary — “because you’re never going to design one single study that gets at every single one of those issues.”
She pointed out that even when different studies were excluded from the subgroup analyses, the main results remained consistent — which made the researchers “much more convinced that these findings are real.”
“When you pull all of the results of every available study together, no matter how you cut it, and if you’re very, very stringent about the quality of the studies, you still end up finding that untreated white coat hypertension is associated with this increased risk, whereas treated white coat effect [is] not,” Cohen said.
Paul Munter, who co-wrote an editorial on the study, said this was an important study because it “synthesizes the most contemporary data” and shows the importance of out-of-office blood pressure monitoring.
“Once people start blood pressure lowering medications, they’re going to be on it for the rest of their lives, and so it’s still useful to have the extra information on someone’s blood pressure before asking them to take medication for the rest of their life,” said Munter, an associate dean for research at the University of Alabama at Birmingham School of Public Health.
Cohen and others are also hoping the research will encourage insurers to cover ambulatory blood pressure monitors, in which patients wear a belt around their body, attached to a cuff on their upper arm, and which take blood pressure readings periodically. Right now, most doctors rely on home blood pressure monitoring, in which doctors entrust patients to take their own readings. That can be flawed — when patients take their own blood pressure readings, they often forget or remove measurements they don’t like from the datasets, making the data less reliable.
But ambulatory monitors are expensive, and few insurers cover them.
Dr. William White, previous president of the American Society of Hypertension, argued that the new data highlights their importance — and their relative value. Preventing cardiac events like strokes or heart attacks could save the health care system far more than the devices cost over time.
“It’s silly to not want to cover this test, because in the long run, it would pay for itself,” he said. “This [study] actually increases knowledge of how important it is to accurately diagnose people. You just need to know what they really are, because if you can’t figure that out, it’s impossible, you’re just guessing.”
For now, Cohen is recommending that those with white coat hypertension adopt a better diet and exercise, while monitoring their blood pressure out of the office regularly, with the important caveat that it is an accurate blood pressure measuring device — a list of which will come out this summer from the American Medical Association.
“There’s no such thing right now as a smartwatch, that can actually check a blood pressure without having a cuff, like an actual blood pressure cuff on it,” Cohen said. “And so it’s just very important to be a savvy consumer about these things.”