Effect of skin tone on the accuracy of the estimation of arterial oxygen saturation by pulse oximetry: a systematic review

Background: Pulse oximetry-derived oxygen saturation (SpO₂) is an estimate of true arterial oxygen saturation (SaO₂). The aim of this review was to evaluate available evidence determining the effect of skin tone on the ability of pulse oximeters to accurately estimate SaO₂. Methods: Published literature was screened to identify clinical and non-clinical studies enrolling adults and children when SpO₂ was compared with a paired co-oximetry SaO₂ value. We searched literature databases from their inception to March 20, 2023. Risk of bias (RoB) was assessed using the QUADAS-2 tool. Certainty of assessment was evaluated using the GRADE tool. Results: Forty-four studies were selected reporting on at least 222 644 participants (6121 of whom were children) and 733 722 paired SpO₂–SaO₂ measurements. Methodologies included laboratory studies, prospective clinical, and retrospective clinical studies. A high RoB was detected in 64% of studies and there was considerable heterogeneity in study design, data analysis, and reporting metrics. Only 11 (25%) studies measured skin tone in 2353 (1.1%) participants; the remainder reported participant ethnicity: 68 930 (31.0%) participants were of non-White ethnicity or had non-light skin tones. The majority of studies reported overestimation of SaO₂ by pulse oximetry in participants with darker skin tones or from ethnicities assumed to have darker skin tones. Several studies reported no inaccuracy related to skin tone. Meta-analysis of the data was not possible. Conclusions: Pulse oximetry can overestimate true SaO₂ in people with darker skin tones. The clinical relevance of this bias remains unclear, but its magnitude is likely to be greater when SaO₂ is lower. Systematic review protocol: International Prospective Register of Systematic Reviews (PROSPERO): CRD42023390723.