WASHINGTON, D.C. (February 23, 2021)—Pulse oximeters, which measure blood oxygen levels, have been widely used during the COVID-19 public health emergency to track a patient’s oxygen saturation, but they may not always be accurate, according to new guidance recently released by the Food and Drug Administration.

Skin color, nail polish, tobacco use, skin temperature and other factors can affect the accuracy of pulse oximeters used to estimate blood oxygen levels, the Food and Drug Administration said in the guidance.

Patients and health care providers should not solely rely on pulse oximeter readings when monitoring illnesses like COVID-19 at home, according to William Maisel, the director of FDA’s Office of Product Evaluation and Quality for medical devices.

The agency’s safety notice comes after increasing concern about racial disparities in the accuracy of pulse oximeter data, driven in part by increased consumer use of the devices during the pandemic.

The FDA acknowledged a study published last year that found pulse oximeters performed worse among Black patients than white patients. That could increase the risk that Black patients with low oxygen levels do not receive needed treatment, concluded the study’s authors, a team from the University of Michigan Medical School.

The FDA also cautioned that over-the-counter oximeters—including smartphone apps that estimate oxygen saturation—that are not reviewed by the agency should not be used for medical purposes.

“Use of OTC oximeters has increased as a result of the COVID-19 pandemic,” the FDA safety communication states. “These products are sold as either general wellness or sporting/aviation products that are not intended for medical purposes, so they do not undergo FDA review.”

The new safety communication from FDA comes less than a month after Democratic Sens. Elizabeth Warren (Massachusetts), Cory Booker (New Jersey) and Ron Wyden (Oregon) wrote to the agency expressing concern pulse oximeters perform worse when measuring blood oxygen levels of patients of color.

“Skin pigment does appear to matter to pulse oximeter measurements, as demonstrated by the 2005 study, a 2007 study and a recent 2020 study which found that low levels of oxygen in the blood of Black patients was nearly three times as likely to be undetected than it was in white patients,” the senators wrote.

The FDA recommends that clinical trials include people with a range of skin colors, but noted Friday that studies are often not designed to detect differences in performance between demographic groups.

“FDA has continued to review the effects of skin pigmentation on the accuracy of these devices, including data from controlled laboratory studies and data from real world settings,” the agency said.