PULSE OXIMETRY SKIN
The only current relevant systematic review, published in 1995, included three studies that explicitly considered the impact of skin pigmentation on pulse oximetry accuracy.
It is an important time to consider the current evidence base for the impact of skin pigmentation on the accuracy of pulse oximetry compared with the gold standard measure of SaO 2. In November 2021, the UK Health Secretary ordered a review into racial bias in medical equipment, including pulse oximeters. Results showed people described as Black had ‘nearly three times the frequency of occult hypoxemia that was not detected by pulse oximetry’ as those described as White. A recent US study analysed retrospective cohort data from more than 10,000 people, comparing where a diagnosis of occult hypoxemia (an SaO 2 of less than 88%) was missed by pulse oximetry. Measurement inaccuracy could have serious clinical implications including the delay of urgent medical care. Higher levels of skin pigmentation could, in theory, affect how light is absorbed, thus possibly affecting the accuracy of pulse oximetry readings.
Pulse oximetry works by beaming light through skin into the blood and inferring an SpO 2 reading from the amount of light absorbed. The reporting of possible bias in pulse oximetry measurement, including due to skin pigmentation, raised a growing concern about the accuracy of oxygen self-monitoring. Many countries have specific guidance or services for home pulse oximetry in line with this recommendation, such as the NHS England COVID service. The current WHO COVID-19 management guideline recommends the ‘use of pulse oximetry monitoring at home as part of a package of care’ for symptomatic people with COVID-19. Pulse oximetry has been widely used during the COVID-19 pandemic, including in non-clinical settings, to detect hypoxemia and inform decisions to escalate care. Pulse oximetry, measuring SpO 2 as a proxy for SaO 2 using a non-invasive and simple device, is frequently used to detect low blood oxygen levels. The gold standard measure of blood oxygen saturation levels (SaO 2) requires a sample of arterial blood and measurement using CO-oximetry. Low blood oxygen saturation, if identified to be hypoxemia, requires medical intervention and has been linked to an increased risk of death. Review protocol registrationīlood oxygen saturation levels require monitoring for health reasons in a wide range of circumstances. The extent of overestimation may be small in hospital settings but unknown in community settings. Pulse oximetry may overestimate oxygen saturation in people with high levels of skin pigmentation and people whose ethnicity is reported as Black/African American, compared with SaO 2. When the extent of measurement bias and precision is considered jointly, pulse oximetry measurements for all the subgroups appear acceptably accurate (with A rms < 4%).
Whilst the extent of mean bias is small or negligible for all subgroups evaluated, the associated imprecision is unacceptably large (pooled SDs > 1%). The bias of pulse oximetry measurements for people with other levels of skin pigmentation or those from other ethnic groups is either more uncertain or suggests no overestimation. Compared with standard SaO 2 measurement, pulse oximetry probably overestimates oxygen saturation in people with the high level of skin pigmentation (pooled mean bias 1.11% 95% confidence interval 0.29 to 1.93%) and people described as Black/African American (1.52% 0.95 to 2.09%) (moderate- and low-certainty evidence). We included 32 studies (6505 participants): 15 measured skin pigmentation and 22 referred to ethnicity. The review was registered with the Open Science Framework ( ). We performed meta-analyses for mean bias (the primary outcome in this review) and its standard deviations (SDs) across studies included for each subgroup of skin pigmentation and ethnicity and used these pooled mean biases and SDs to calculate accuracy root-mean-square ( A rms) and 95% limits of agreement. We searched Ovid MEDLINE, Ovid Embase, EBSCO CINAHL,, and WHO International Clinical Trials Registry Platform (up to December 2021) for studies with SpO 2–SaO 2 comparisons and measuring the impact of skin pigmentation or ethnicity on pulse oximetry accuracy. We systematically reviewed the effects of skin pigmentation on the accuracy of oxygen saturation measurement by pulse oximetry (SpO 2) compared with the gold standard SaO 2 measured by CO-oximetry. During the COVID-19 pandemic, there have been concerns regarding potential bias in pulse oximetry measurements for people with high levels of skin pigmentation.
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