Pulse oximeters have become widely used devices for measuring blood oxygen levels, particularly since gaining prominence during the COVID-19 pandemic. However, research has increasingly documented limitations in these handheld tools, with multiple studies indicating they overestimate blood oxygen readings when used on patients with darker skin tones. This inaccuracy can mask serious health conditions and contribute to healthcare disparities.
A recent retrospective study published in the Annals of the American Thoracic Society examined five years of data from Johns Hopkins Hospital’s intensive care units and found an unexpected pattern: the same make of pulse oximeter was not consistent in its accuracy over time. Rather than consistently overestimating readings, the devices gradually shifted to underestimating blood oxygen levels across all patients at higher oxygen levels, though the inaccuracies remained worse for patients of color. Researchers conducting the study acknowledged uncertainty about the cause of this shift, describing pulse oximeters as a “black box” whose mechanisms remain poorly understood.
The study was prompted by findings from an earlier FDA-funded study called EquiOx, which paradoxically found that pulse oximeters underestimated rather than overestimated blood oxygen levels in patients with darker skin tones. Both findings create clinical challenges: if devices consistently erred in one direction, physicians could adjust their practices accordingly. The inconsistency makes interpretation and clinical decision-making significantly more difficult, particularly given the devices’ critical role in patient care.
Manufacturer Masimo stated it was unaware of any sensor, software, or manufacturing changes during the study period that would explain the reported results, and noted multiple factors can affect readings beyond skin tone. Researchers from other institutions suggest the problem extends beyond skin pigmentation alone, with conditions like anemia, cardiovascular disease, and liver disease potentially affecting accuracy. The mounting evidence has raised questions about whether current pulse oximeters are adequate for their widespread clinical use, and whether next-generation devices will be able to address the complex sources of racial bias in their readings.
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