An app that measures your blood pressure through your smartphone is "highly inaccurate," according to a research letter published Wednesday in JAMA Internal Medicine. The app, Instant Blood Pressure, missed high blood pressure levels in nearly four out of five people, the researchers found.
The app's manufacturer fired back on Wednesday, arguing that the study was based on faulty methodology and thus invalid. The lead researcher defended the findings.
"This isn't something I want my patients using," says Dr. Tim Plante, a general internal medicine fellow at Johns Hopkins University and lead author of the letter.
The app is no longer available for sale, but it was popular between 2014 and 2015, with people buying 148,000 units, according to Plante and his colleagues. He's concerned that those who bought it will keep using it.
"If you have people who are using an inaccurate device like Instant Blood Pressure at home, and telling their doctor, 'my blood pressure is OK,' you could miss a risky high reading and develop complications from that down the road," Plante says.
Uncontrolled high blood pressure can lead to heart attacks and strokes.
As part of their study, researchers tested the blood pressure levels of 85 people with hypertension in August and September 2015. They did this four times per patient — twice with a research-grade blood pressure cuff and twice with the Instant Blood Pressure app.
The app doesn't require any other hardware; to use it, you press your phone against your chest and place your right finger over the phone's camera lens.
Blood pressure is typically recorded as the ratio of systolic to diastolic pressure. The researchers found that when they used the app, the systolic pressure, which measures the pressure in the arteries when the heart beats, was an average of 12 millimeters of mercury off from the results they got using the cuff. Their results for diastolic pressure, which measures the pressure in the arteries between heartbeats, was an average of 10 millimeters of mercury off.
Among people the researchers identified as having elevated blood pressure levels by using a research-grade blood pressure monitor, "78 percent of those had normal blood pressure when you checked it with the Instant Blood Pressure app," says Plante.
Ryan Archdeacon, co-founder and CEO of AuraLife, which makes Instant Blood Pressure, claims the company updated its algorithm for estimating blood pressure fives times during the study period and 18 times since then. He adds that the algorithm updates were both "incremental" and "pivotal," rendering the app more accurate.
Plante and the other researchers "failed to control for the most critical factor in performing this experiment: ... the version of the blood pressure algorithm itself," Archdeacon argues in a written statement.
"Regarded members of the scientific community would view the failure to implement this critical control as grounds for invalidating the study in its entirety," Archdeacon adds.
Archdeacon also says the app only produces blood pressure values within a specific range and says the researchers did not acknowledge this in the study. "This is scientific misconduct, is unethical, and is grounds for invalidating the entire study," he charges.
Plante and his team are refusing to concede any of Archdeacon's points. The researchers "don’t think they change the interpretation of the study and we stand by our findings," says Plante.
The app underwent internal testing by the manufacturer, but Plante adds that AuraLife's internal tests of the app were never independently validated.
Instant Blood Pressure's website says that people should not rely on the app for medical advice or diagnosis. It says the app "is for recreational use only" and "it is not a replacement or substitute for a cuff or other blood pressure monitor."
Plante says the research highlights the promise and pitfalls of mobile health technology.
Health apps are experiencing "growing pains," he says, because while some can help people lead healthier lives, others can put patients at risk. And it can be hard to sort out which ones fall into which category, even for medical professionals, he says.
"I want to tell people that they should ask their doctor about what apps they should use, but I don't think doctors know," he says.
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This story has been updated.