Study finds Johns Hopkins pulse oximeters shifted from over- to under-reading oxygen levels

A retrospective analysis of five years of intensive-care data at Johns Hopkins Hospital revealed that its pulse oximeters transitioned from overestimating to underestimating arterial oxygen levels, with the greatest inaccuracies observed in patients of color at higher saturations. The study, published in the Annals of the American Thoracic Society, could not pinpoint the cause of the shift, and the device maker Masimo said no sensor, software, or manufacturing changes occurred during the period.

Masimo highlighted that placement, signal quality, and patient perfusion also influence readings and cited internal studies showing no skin-tone bias. Clinicians now face uncertainty about how to interpret oximeter data, as both over- and under-estimation can lead to inappropriate treatment. Experts compare the devices to a broken clock, noting that without a consistent error pattern, adjustments are difficult. The findings add to growing evidence that pulse oximeter performance is affected by factors beyond skin pigmentation, such as anemia or cardiovascular disease.