Ottawa – Even as doctors are increasingly relying on home blood pressure monitoring to manage patients with hypertension, a new small study found that these devices may not be accurate enough.
Researchers say that in about 70 percent of the time, home monitors were not accurate within 5 mmHg, which is considered clinically important. Thirty percent of the time, the devices were 10 mmHg off the mark.
The lead researcher Jennifer Ringrose of the University of Alberta in Canada said that hypertension, or high blood pressure, is the number one cause of death and disability in the world.
“Guidelines are recommending that clinicians rely more on automatic and home blood pressure readings to diagnose and monitor high blood pressure,” she told Reuters Health by email. “We need to make sure these home blood pressure readings are accurate.”
Ringrose and her colleagues gauged the accuracy of home blood pressure monitors used by 85 patients and tested for differences between upper-arm versus wrist with different devices.
Two observers tested each patient simultaneously, taking a total of nine blood pressure measurements and alternating between the device used at home and a standardized cuff used in a doctor’s office.
Blood pressure is measured with two numbers: systolic pressure when the heart pumps blood and diastolic pressure when the heart rests between beats. Blood pressure below 120 mmHg systolic/80 mmHg diastolic is considered healthy. Pressure above 140/90 mmHg is considered high.
The researchers found that home monitors were more often wrong for systolic pressure. For 54 percent of patients, that measurement differed by 5 mmHg from the professional device; for 20 percent it was wrong by 10 mmHg, and for 7 percent it was off by 15 mmHg or more. With diastolic pressure, the same was true of 31 percent 12 percent and 1 percent of patients.
Researchers concluded that arm size and gender were the main predictors of a systolic blood pressure difference, with men typically having a larger difference. Also, older age, larger arm circumference, hard cuff design, and older device models were linked with diastolic blood pressure differences.
The study authors wrote in the American Journal of Hypertension that age and stiffness of blood vessels, for example, can make a significant difference if blood pressure monitors are not calibrated for the patient using it.