The pulse oximeter is a device that estimates a person’s oxygen saturation level, a measure of the oxygen concentration in their blood, by shining light through their tissue, typically a fingertip or an earlobe (Fig. 1). As highlighted by the COVID-19 pandemic, accurate pulse-oximeter readings can be crucial for clinical decisions, especially when arterial blood-gas tests — the gold standard for determining oxygen saturation levels — are not available. But these devices give readings that are often less accurate for people who have dark skin, and this shortcoming has led to medical practices that only exacerbate the problem, making pulse oximetry emblematic of the broader issue of racial bias in medicine. The first step towards a solution must involve an orchestrated effort from those who design, use and regulate these devices.

Driven by clinical experiences early in the pandemic, Sjoding et al.¹ published a retrospective report showing that pulse oximeters overestimate the true oxygen saturation of Black people. This inaccuracy means that diagnoses of hypoxaemia, the condition of having low levels of oxygen in one’s blood, are approximately three times more likely to be missed in Black patients than in white patients. Misdiagnosed patients are said to have occult hypoxaemia when arterial blood-gas tests indicate oxygen saturation levels of less than 88% (signalling hypoxaemia), despite pulse oximeters measuring a healthy oxygenation of more than 92%.