The U.S. FDA is warning healthcare providers that pulse oximeters can produce inaccurate or misleading results, particularly for Black patients, reports The Hill

Pulse oximeters have become an essential piece of medical equipment in the coronavirus pandemic since monitoring oxygen levels is crucial when a person has COVID-19.

But a study released in December found that oximeters were more likely to give inaccurate or misleading results when used on Black patients. The device works by shining a red light through a patient’s fingertip, and inaccurate oxygen readings were reported three times more often with Black patients.

The study’s lead author, Michael Sjoding, said that the inaccuracies were not occurring “a lot,” accounting for roughly 12% readings, but that that amount could still be “really impactful.”

Read more in The Hill.