The researchers outlined their findings on digital health startup AuraLife’s Instant Blood Pressure (IBP) app in a study published in the medical journal JAMA Internal Medicine. The authors tested out the app on 85 participants and found that it had a tendency to inform users that their blood pressure was in the normal range when it was actually quite high.

“The low sensitivity for hypertensive measurements means that approximately four-fifths (77.5%) of individuals with hypertensive BP levels will be falsely reassured that their [blood pressure] is in the nonhypertensive range,” wrote the researchers. “Our study has both clinical and public health relevance. While IBP recently became unavailable for unclear reasons, it is installed on a vast number of iPhones.”

IBP was available on the iPhone app store between June of 2014 and July of 2015 and cost $4.99. It functions by having users place the upper edge of their smartphones on their chest while covering up the camera with their right index finger.

According to the study authors, the app was a top 50 best-seller on the iPhone for 156 days, and there are several other apps which serve similar functions that are still currently available on iPhone and Android app stores.

AuraLife, the company behind the app, says that it is “on a mission to democratize access to knowledge and insight about individual well-being anytime, anywhere” on its website. But the company also warns that IBP is “not a replacement or substitute for a cuff” and shouldn’t be relied upon for medical advice or a diagnosis.

While mHealth technology has been heralded by some for its potential to conveniently empower patients with data, regulators have found themselves playing catch-up with the tech and have had to crack down on certain apps.

Last year, the FTC reached settlements with the marketers of “melanoma detection” apps like MelApp and Mole Detective for making unsupported claims. The FDA regulates mobile medical apps using the same general guidance it applies to medical devices.

There are more than 165,000 mobile health apps available on the market, according to IMS Health, and the sector could be a $26 billion industry by the end of 2017.

Responding to a request for comment from Fortune, Auralife’s co-founder and CEO Ryan Archdeacon said:

We were shocked to have identified critical deficiencies and inaccuracies in the study control design and data analysis that cause it to inaccurately portray the performance of Instant Blood Pressure. We have our own data.

We welcome third party researchers taking an active interest in assessing our technologies. Further, we believe open discussion with researchers is important and we welcome the opportunity to provide our feedback.

With that said we do believe that three critical items need to be taken into consideration. These concerns were shared with the authors late on March 1st and on the morning of March 2nd conversations between AuraLife and the authors’ team were initiated. Those conversion are ongoing and we are awaiting the Plante et. al. team’s response.