As many as 20 per cent of Canadians diagnosed with high blood pressure may not have the condition, all because they’ve been misdiagnosed by doctors using outdated blood pressure monitors.

So says a study by researchers at the University of Montreal’s Hospital Research Centre (CRCHUM), which found that more than half of the family doctors in Canada are still using manual devices to measure blood pressure instead of more precise automated machines.

For decades, doctors have used devices called sphygmomanometers and tensiometers to measure blood pressure. They typically consist of a cuff that is manually inflated and a reading given on a mercury-filled manometer.

But automatic electronic blood pressure monitors, known as oscillometric devices, tend to be more accurate and easier to use. That’s why, in 2016, guidelines from the Canadian Hypertension Education Program (CHEP) recommended that electronic measurement is preferable to manual measurement for screening for high blood pressure (known as hypertension).

Electronic machines, such as the ones offered in pharmacies, are also good for monitoring high blood pressure, the recommendations said.

Many doctors’ offices have already switched over to the automatic devices, but Janusz Kaczorowski, a medical sociologist at CRCHUM, wanted to know how many doctors were still using older methods. So last spring, his research team conducted a survey among Canadian family doctors to ask them about their use of blood pressure monitors.

Of the 769 physicians who responded, 52 per cent said they used manual BP measurements to screen for high blood pressure. Only 43 per cent said they routinely used an automatic device.

It’s encouraging that more and more family physicians are moving away from manual office BP measurement for diagnosing high blood pressure, Kaczorowski says, but it’s discouraging that more accurate methods are not being used more often.

Manual blood pressure measurement can be precise but only if it is done properly, which is rarely the case, Kaczorowski and his team note.

Researchers have long noted something called “white-coat syndrome,” which refers to temporarily high blood pressure from the stress of being in a doctor’s office and interacting with the physician.

To take blood pressure the right way, a 12- to 15-minute period is required to allow patients to relax, he said. But the average family doctor visit lasts only 10 minutes. Automated devices can get the best reading because they can account for “white-coat syndrome,” he says.

“Clinicians should use automatic devices," Kaczorowski said. "They are more expensive but more precise because they take several measurements.”

Kaczorowski worries there may be Canadian patients who are taking medications they don’t need for hypertension, all because their blood pressure was measured incorrectly.

“If people who take high-blood-pressure medication had their blood pressure measured incorrectly, the financial implications are considerable, in addition to the side effects, which could be avoided,” he said in a statement.

The full results of the study appear in the online version of the journal Canadian Family Physician.