70% of Home Blood Pressure Monitors Inaccurate, Finds Study

Many patients of high blood pressure or hypertension keep a monitor at home these days to check their readings but a new study by UAlberta warns that 70% of readings from home BP monitors are unacceptably inaccurate.

“High blood pressure is the number one cause of death and disability in the world,” said medical researcher Jennifer Ringrose, who led the research study. “Monitoring for and treating hypertension can decrease the consequences of this disease. We need to make sure that home blood pressure readings are accurate.”

Ringrose and her team tested dozens of home monitors and found they weren’t accurate within five mmHg about 70 percent of the time. The devices were off the mark by 10 mmHg about 30 per cent of the time.┬áThe findings are crucial as millions of patients keep monitoring their blood pressure using such devices at home and report the results back to their doctor.

However, the researchers say steps can be taken to minimize inaccurate readings.

“Compare the blood pressure machine measurement with a blood pressure measurement in clinic before exclusively relying upon home blood pressure readings,” advised Ringrose. “What’s really important is to do several blood pressure measurements and base treatment decisions on multiple readings.”

Study co-author Raj Padwal, a UAlberta professor of medicine, added that no one should have drugs started or changed based on one or two measurements taken at a single point in time. In 2015 Canada gave certain guidelines endorsing greater use of home blood pressure monitoring with 28 measurements over one week for home devices.

Blood pressure monitoring (Image: American Heart Association)

The study examined the results of 85 patients and compared the results with the gold standard–two observers taking several BP readings simultaneously, without the knowledge of the other and a third person ensuring agreement between both observers’ readings.

While the average difference between the home monitors and the gold standard measurements was acceptable, the majority of individual devices demonstrated clinically-relevant inaccuracy, said the team. Moreover, the readings were more inaccurate in men than in women.

But the researchers believe there are many factors for their findings. “Arm shape, arm size, the stiffness and age of blood vessels, and the type of blood pressure cuff are not always taken into account when a blood pressure machine is designed and validated,” said Padwal. “Individual differences, such as the size, age and medical background of the person using the blood pressure monitor are also contributing factors.”

The researchers say it’s difficult to determine precisely why the inaccuracies are occuring in home monitors owing to proprietary information kept secret by the manufacturer.

The study was published in the American Journal of Hypertension.

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