What is the pulse oximeter? FDA says key medical device used in Covid-19 fight may not work on Black patients
Pulse oximeters that measure the percentage of oxygen in the blood are more likely to be inaccurate for people with dark skin
Many people with coronavirus have low levels of oxygen in their blood even when they feel well, which can be an early warning sign that medical care is needed, say experts. Accordingly, the Covid-19 pandemic has caused a spike in the use of pulse oximeters, which are medical devices that monitor the level of oxygen in a patient’s blood and alert doctors and nurses if oxygen levels drop below safe levels, enabling quick intervention. However, the US Food and Drug Administration (FDA) has now warned that pulse oximeters may lead to inaccurate results for people with dark skin.
The FDA statement comes in light of a study by Michigan Medicine researchers who found that the pulse oximeter may be less accurate in Black patients than in White patients.
“The Covid-19 pandemic has caused an increase in the use of pulse oximeters, and a recent report suggests that the devices may be less accurate in people with dark skin pigmentation. The FDA is informing patients and health care providers that although pulse oximetry is useful for estimating blood oxygen levels, pulse oximeters have limitations and a risk of inaccuracy under certain circumstances that should be considered,” states the agency. It adds, “Patients with conditions such as Covid-19 who monitor their condition at home should pay attention to all signs and symptoms of their condition and communicate any concerns to their healthcare provider.”
The FDA says that the study has some limitations as it relies on previously collected health record data from hospital inpatient stays and “could not statistically correct for all potentially important confounding factors.” “However, the FDA agrees that these findings highlight a need to further evaluate and understand the association between skin pigmentation and oximeter accuracy,” it emphasizes.
The US Centers for Disease Control and Prevention (CDC) has also updated its Covid-19 clinical guidance, cautioning that new information indicates that skin pigmentation can affect the accuracy of the devices.
What did the study find?
A pulse oximeter fits on the end of a patient’s finger to measure the percentage of oxygen in the blood. They are often used in hospitals and clinics and can be bought to use at home.
Using data from patients hospitalized at Michigan Medicine and an older dataset of patients hospitalized in multiple intensive care units across the country, the team compared results from pulse oximeters and arterial blood gas measurements (which measures oxygen saturation directly through a blood test) in patients who identified as either Black or White.
“We wanted to know: when the pulse oximeter is measuring between 92 and 96%, how often is the oxygen saturation actually less than 88% on arterial blood gas?” writes Dr Michael Sjoding from the University of Michigan Medical School. A reading of below 88% is generally where most physicians start to take notice and intervene.
The authors identified a reoccurring discrepancy between readings from the pulse oximeter and arterial blood gas measurements. The analysis reveals that Black patients were three times as likely to have a significant discrepancy in the pulse oximeter readings. In other words, Black patients had three times the frequency of low oxygen levels in the blood as detected by blood gas measurements but not detected by pulse oximetry, when compared to White patients.
“Twelve percent of the time, when Black patients had a pulse oximeter reading in this safe range, their actual saturation on an arterial blood gas was below 88%. In White patients, this discrepancy occurred 4% of the time,” say findings published in the New England Journal of Medicine (NEJM).
What does the FDA recommend?
According to the agency, multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish. It is advising Americans not to rely only on a pulse oximeter to assess health conditions or oxygen levels.
“When taking pulse oximeter measurements, pay attention to whether the oxygen level is lower than earlier measurements, or is decreasing over time. Changes or trends in measurements may be more meaningful than one single measurement. Over-the-counter products that you can buy at the store or online are not intended for medical purposes,” suggest experts.
The agency explains that while in many cases, the level of inaccuracy may be small and not clinically meaningful, there is a risk that an inaccurate measurement may result in unrecognized low oxygen saturation levels. “Therefore, it is important to understand the limitations of pulse oximetry and how accuracy is calculated and interpreted,” it adds.
When monitoring oxygen levels at home, the FDA is asking people to pay attention to other signs or symptoms of low oxygen levels, such as bluish coloring in the face, lips, or nails; shortness of breath, difficulty breathing, or a cough that gets worse; restlessness and discomfort; chest pain or tightness; and fast or racing pulse rate. “Be aware that some patients with low oxygen levels may not show any or all of these symptoms. Only a healthcare provider can diagnose a medical condition such as hypoxia (low oxygen levels),” the statement notes.