The impact of skin tone on the performance of pulse oximeters used by the National Health Service COVID oximetry @home scheme: a measurement and diagnostic accuracy study

Abstract

Objectives: to assess the impact of skin tone on the measurement and diagnostic accuracy of five fingertip pulse oximeters used by patients in the NHS England COVID oximetry @home scheme.

Design: multi-centre diagnostic accuracy study (EXAKT).

Setting: twenty-four intensive care units in England between June 2022 and August 2024.

Participants: 903 critically ill adults on intensive care units screened for or enrolled into a trial evaluating different approaches to oxygen therapy.

Interventions: pulse oximetry-derived peripheral oxygen saturation (SpO2) measurements were compared with paired arterial oxygen saturation (SaO2) measurements from arterial blood analysed by co-oximetry (gold-standard). Skin tone (individual typology angle, ITA) was objectively measured using a hand-held spectrophotometer.

Main outcome measures: pulse oximeter measurement accuracy was assessed for bias, precision and overall accuracy. Diagnostic accuracy for identifying SaO2 ≤92% was assessed by false negative and positive rates for SpO2 using thresholds of ≤92% and ≤94%, and the area under the receiver operating characteristic curve, and by presence of occult hypoxaemia (SaO2 <88% with SpO2 >92%).

Results: 11,018 paired SpO2-SaO2 measurements were analysed. All tested pulse oximeters overestimated at lower values and underestimated at higher values of SaO2. SpO2 readings were, on average, 0.6–1.5 percentage points higher for patients with darker (ITA −44°) than lighter (ITA 46°) skin tone. At both SpO2 thresholds assessed, false negative rates increased with darker skin tones; the proportion of SpO2 measurements >94% despite a paired SaO2 ≤92% ranged from 5.3–35.3 percentage points higher for patients with darker than lighter skin tone (7.6–62.2% vs 1.2–26.9%, rate ratio 2.3–7.1). Conversely, false positive rates decreased with darker skin tones.

Conclusions: five pulse oximeters, provided by the NHS England COVID oximetry @home scheme, yielded higher SpO2 measurements for patients with darker, compared with lighter, skin tones that could translate into potentially clinically important differences in false negative and positive rates for detecting hypoxaemia.

Trial registration: ClinicalTrials.gov NCT05481515

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