It’s no longer on the market, but back in 2014, a blood pressure app was one of the top 5 apps. Now researchers have shown that the Instant Blood Pressure app, which claimed to take BP measurements for health management, was inaccurate approximately 80% of the time.

Made by Aura Labs, the app supposedly measured blood pressure simply by placing a cellphone on the chest with a finger. According to researchers, led by Dr. Timothy Plante, a fellow in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine, the app was downloaded more than 100,000 times and is still functional on phones. Aura Labs charged between $2 and $5, meaning that developers made quite a bit of money from an unvalidated product.

The level of inaccuracy is what researchers say is truly disturbing. Plante notes that the app misses high blood pressure in eight out of 10 patients, potentially putting users risk.

“Because this app does such a terrible job measuring blood pressure,” says Plante, “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.”

The study was conducted by Plante and Dr. Seth Martin, an assistant professor in the Division of Cardiology at the Johns Hopkins University School of Medicine. They recruited 85 adult volunteers among patients and staff members in clinics associated with Johns Hopkins Medicine. The participants self-reported a range of body mass measurements, races and ethnicities, all factors known to influence blood pressure.

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.

iMedical Apps published a story on this app in 2014, noting some inconsistencies and red flags. In 2015 the app was removed from the market, with no explanation.

Martin and Plante note that mobile health smartphone applications are becoming more commonplace, and many have the potential to greatly improve health by putting personalized medical resources and information literally in the hands of patients through cellphones. Snake oil salesmen could damage the reputation of many legitimate apps.

“We think there is definitely a role for smartphone technology in health care, but because of the significant risk of harm to users who get inaccurate information, the results of our study speak to the need for scientific validation and regulation of these apps before they reach consumers.”