Home blood pressure monitors were not accurate within five mmHg about 70% of the time. The devices were off the mark by 10 mmHg about 30% of the time.
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‘Home blood pressure readings were more inaccurate in men than in women. These monitoring devices should be accurate to prevent serious complications in patients.’
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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. 
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The findings are extremely relevant given millions of patients are asked to monitor their blood pressure through a device at home and report the results back to their doctor.
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. Taking home readings empowers patients and is helpful for clinicians to have a bigger picture rather than just one snapshot in time."
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 unless the measurements are clearly elevated.
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The study examined the results of 85 patients. The researchers compared the results of the volunteers' home monitors with the gold standard--two observers taking several blood pressure measurements simultaneously, blinded to one another, with a third person ensuring agreement between both observers' readings.
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"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 occurring in home monitors because they don't have access to the various formulas the devices use to determine blood pressure--information which is considered proprietary and kept secret by the manufacturer. They believe a greater effort needs to be made among industry and academia to develop more highly accurate devices in the future.
The study was published in the American Journal of Hypertension.
Source-Eurekalert