The effects of skin pigmentation on the accuracy of pulse oximetry in measuring oxygen saturation: a systematic review and meta-analysis
Authors: Shi Chunhu , Goodall Mark , Dumville Jo , Hill James , Norman Gill , Hamer Oliver , Clegg Andrew , Watkins Caroline Leigh , Georgiou George , Hodkinson Alexander , Lightbody Catherine Elizabeth , Dark Paul , Cullum Nicky 
Published: February 2022

Background

Pulse oximetry was widely used in hospitals and at home to monitor blood oxygen during the COVID-19 pandemic. There have been concerns regarding potential bias in pulse oximetry measurements for people with dark skin. We aimed to assess the effects of skin pigmentation on the accuracy of oxygen saturation measurement by pulse oximetry (SpO2) compared with the gold standard SaO2 measured by CO-oximetry.

Methods

We searched Ovid MEDLINE, Ovid Embase, and EBSCO CINAHL Plus (up to December 2021), as well as ClinicalTrials.gov and World Health Organization International Clinical Trials Registry Platform (up to August 2021). We identified studies comparing SpO2 values in any population, in any care setting, using any type of pulse oximeter, with SaO2 by standard CO-oximetry; and measuring the impact of skin pigmentation or ethnicity on pulse oximetry accuracy. 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 level of skin pigmentation and ethnicity. We calculated accuracy root-mean-square (Arms) and 95% limits of agreement based on pooled mean bias and pooled SDs for each subgroup.

Results

We included 32 studies (6505 participants); 27/32 (84.38%) in hospitals and none in people’s homes. Findings of 14/32 studies (43.75%) were judged, via QUADAS-2, at high overall risk of bias. Fifteen studies measured skin pigmentation and 22 referred only to ethnicity. Compared with standard SaO2 measurement, pulse oximetry probably overestimates oxygen saturation in people with dark skin (pooled mean bias 1.11%; 95% confidence interval 0.29% to 1.93%) and people described as Black/African American (pooled mean bias 1.52%; 0.95% to 2.09%) (moderate- and low-certainty evidence). These results suggest that, for people with dark skin, pulse oximetry may overestimate blood oxygen saturation by around 1% on average compared with SaO2. The bias of pulse oximetry measurements for people with other levels of skin pigmentation, or those from the White/Caucasian group is more uncertain. The data do not suggest overestimation in people from other ethnic groups such as those described as Asian, Hispanic, or mixed ethnicity (pooled mean bias 0.31%, 0.09% to 0.54%), but this evidence is low certainty. Whilst the extent of mean bias is small or negligible for all the subgroups of population evaluated, the associated imprecision is unacceptably large (with the pooled SDs > 1%). Nevertheless, when the extents of measurement bias and precision are considered jointly in Arms, pulse oximetry measurements for all the subgroups appear acceptably accurate (with Arms < 4%).

Conclusions

Low-certainty evidence suggests that pulse oximetry may overestimate oxygen saturation in people with dark skin and people whose ethnicity is reported as Black/African American, compared with SaO2, although the overestimation may be quite small in hospital settings. The clinical importance of any overestimation will depend on the particular clinical circumstance. Pulse oximetry measurements appear accurate but imprecise for all levels of skin pigmentation. The evidence relates to clinician-measured oximetry in health care environments and may not be reflected in home pulse oximetry where other factors may also influence accuracy.

Author summary

Why was this study done?

Pulse oximetry was widely used in hospital and at home to measure blood oxygen levels during the COVID-19 pandemic.

There was uncertainty as to whether skin pigmentation affects the accuracy of pulse oximetry measurements.

What did the researchers do and find?

We assessed, via systematic review, the effects of skin pigmentation on the accuracy of pulse oximetry measurement (SpO2) compared with SaO2 measured by standard CO-oximetry.

In people with dark skin, oxygen saturation measured in hospital by pulse oximetry may be overestimated by an average of 1% compared with gold standard SaO2, however, the evidence is of low certainty.

The accuracy of pulse oximetry measured compared with standard SaO2 is quite uncertain for people with light or medium levels of skin pigmentation and for people from ethnic groups other than those described in papers as Black or African American.

Pulse oximetry measurements appear to have acceptable overall accuracy (with Arms< 4%) for all subgroups of population evaluated whilst the variation of oximetry readings appear unacceptably wide (with the pooled SDs > 1%).

What do these findings mean?

Hospital measured pulse oximetry may overestimate oxygen saturation in people with dark skin compared with SaO2 by approximately 1%.

The implications of this finding in different clinical scenarios will vary but could be clinically important. Impacts are likely to be at the thresholds of being diagnosed as having hypoxaemia where even a small SpO2 overestimation could lead to clinically important hypoxaemia remaining undetected and untreated.

How these findings extrapolate to community and home care settings is unclear.