Measuring blood pressure with a portable 24-hour monitoring device is a more accurate way of assessing people’s risk of premature death from cardiovascular disease than measuring it during a single visit to a doctor’s office, according to a large study published recently in the New England Journal of Medicine (NEJM).
The study also found that people are at a greater risk of an early death from cardiovascular disease when their blood pressure measures high on a home monitoring device but not at the clinic.
“This research is a clear game-changer, as for the first time, it definitely shows that blood pressure measured regularly during a 24-hour period predicts the risk of heart disease, stroke and death much better than blood pressure measured in a doctor’s surgery or clinic,” said Dr. Bryan Williams, the study’s senior author and chair of medicine at University College London, in a released statement.
“With a much more accurate assessment of a patient’s blood pressure, doctors will be able to provide the most effective treatments at the earliest opportunity, which will save many more lives,” he added.
The study used data collected on 63,910 patients at 223 medical clinics across Spain. All the patients had symptoms that met medical-guideline recommendations for 24-hour blood pressure monitoring.
The patients had two blood pressure readings taken in the clinic. They were also given a blood pressure monitoring device to wear at home for 24 hours. The device measured and recorded blood pressure every 20 to 30 minutes.
Based on these readings, the patients were divided into four groups:
- Those with “white coat” hypertension — high blood pressure readings while in the clinic but not while wearing the 24-hour monitor
- Those with “masked” hypertension — high blood pressure readings while wearing the 24-hour monitor but not while in the clinic
- Those with sustained high blood pressure — high blood pressure readings both in the clinic and at home
- Those with no high blood pressure, either in the clinic or at home
The patients were followed for an average of almost five years. During that period, 3,808 of them died of all causes, and 1,295 died of heart attacks, stroke, heart failure and other cardiovascular causes.
The study found that the blood pressure readings from the 24-hour home-monitoring devices were 50 percent more accurate at predicting a patient’s risk of early death than the readings made in the clinics.
That didn’t mean, however, that the clinic readings were not helpful. High blood pressure measurements in the clinic were also predictive of an early death. They just weren’t as predictive as the home devices.
The study also found that masked hypertension — high blood pressure detected on the home devices but not in the clinic — was associated with the highest risk of death. That increased risk may be because the masking led to delays in diagnosing the condition, William and his colleagues suggest. The longer high blood pressure remains undiagnosed and untreated, the greater the damage it can do to the blood vessels and the heart.
Limitations and implications
The study comes with several important caveats. As an observational study, it can’t prove that 24-hour blood pressure monitoring is better than clinic readings at accurately diagnosing high blood pressure and predicting cardiovascular risk. Other factors, not addressed in the study, might explain the results.
In addition, the blood pressure readings in the study were taken at single moments in time (one clinic visit and one 24-hour period). This factor limits the prognostic power of the readings, the study’s authors point out.
Another caveat can be found in the study’s conflict of interest statement, where Williams is listed as an adviser to a company that makes portable blood pressure devices.
Still, this research supports other — albeit smaller — studies that have also shown that measuring blood pressure over the course of a day often provides a truer assessment of a person’s blood pressure status than a single reading in a doctor’s office.
Indeed, the American Heart Association (AHA), as well as other medical organizations, now recommends that people with high blood pressure — and certain other groups of people who may be at risk of having the condition — monitor their blood pressure at home.