New York, Mar 3 (IANS): A popular smartphone app purported to accurately measure blood pressure in an instant actually fails to detect high blood pressure in eight out of 10 patients, thereby potentially putting users' health at risk, an alarming study has found.

Although the app, called Instant Blood Pressure, is no longer available for purchase, it was downloaded more than 100,000 times and is still functional on phones, the researchers said.

"Because this app does such a terrible job measuring blood pressure, it could lead to irreparable harm by masking the true risk of heart attacks and strokes in people who rely on the accuracy of this information," said one of the researchers Timothy Plante from Johns Hopkins University School of Medicine in the US.

The findings appeared online in the journal JAMA Internal Medicine.

According to the researchers, blood pressure is best measured using the well-established technique of inflating a cuff attached around the brachial artery in the arm to detect the force of blood flowing when the heart is beating and at rest.

Either a trained medical professional or a machine "listens" to sounds from the brachial artery as blood flows under variable pressure from the cuff.

The popular smartphone app purports to accurately measure blood pressure simply by placing a cellphone on the chest with a finger over the built-in camera lens

The researchers conducted the study on the app "because of the absence of any rigorous scientific testing” and “there was no evidence that it worked or didn't work."

To conduct such testing, the researchers recruited 85 adult volunteers among patients and staff members in clinics associated with Johns Hopkins Medicine.

Each participant had his or her resting blood pressure measured twice using a reliable automated blood pressure monitor commonly used in research studies to avoid measurer variation or error.

Participants also used the app to measure their own blood pressure twice on the same day.

Results showed that blood pressures measurements from the app were overwhelmingly inaccurate.

Close to 80 percent of those with clinically high blood pressure, defined as 140/90 millimetres of mercury or above, measured by the automated blood pressure monitor showed normal blood pressure with the app.

The authors said that it is unclear how the app arrives at a blood pressure number.

Rather than attempting to measure true blood pressure, the app gives a population-derived estimate based on the user's age, sex, height, weight and heart rate, the latter of which could be detected by the phone's microphone, the researchers suggested.