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 (National Health Service) England COVID Oximetry @home scheme.
DESIGN: Measurement and diagnostic accuracy study (exploring pulse oximeter accuracy across skin tones-EXAKT).
SETTING: Twenty four intensive care units in England between June 2022 and August 2024.
PARTICIPANTS: 903 critically ill adults admitted to 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) was objectively measured using a handheld 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 false positive rates for SpO2 using thresholds of =92% and =94%, and the area under the receiver operating characteristic curve, and by the 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. On average, SpO2 readings were 0.6-1.5 percentage points higher for patients with darker skin tone (individual typology angle -44°) than for those with lighter skin tone (46°). 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 to 35.3 percentage points higher for patients with darker skin tones than for those with lighter skin tones (7.6-62.2% v 1.2-26.9%, rate ratio 2.3-7.1). By contrast, 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 skin tones compared with those with lighter skin tones, which could translate into potentially clinically important differences in false negative and false positive rates for detecting hypoxaemia.
TRIAL REGISTRATION: ClinicalTrials.gov NCT05481515.
| Discipline Area | Score |
|---|---|
| Intensivist/Critical Care |  |
| Family Medicine (FM)/General Practice (GP) | |
| General Internal Medicine-Primary Care(US) | |
| Respirology/Pulmonology |  |
| Internal Medicine | |
A well done study confirming that across different pulse oximeters, darker skin tone results in higher pulse oximetry readings given the same arterial oximetry level. This may result in those with darker skin tone who have low O2 sats being misdiagnosed as having normal O2 sats. It's important to note that this results reflects the effect of skin tone and not race.
Clinicians should maintain heightened suspicion for occult hypoxemia in patients with darker skin tones and consider lower SpO2 thresholds for treatment decisions or obtain arterial blood gas measurements when clinical concern exists. This study adds important objective evidence to a growing body of literature documenting racial disparities in pulse oximetry performance and their potential contribution to health inequities. Clinicians are now being taught that a reading of 92% in a dark-skinned patient should be treated with the same level of concern as an 89% in a light-skinned patient.
Home pulse oximeters are now very frequently used and widely available, especially since COVID. Reports suggest that readings in patients with darker skin tones overestimate oxygenated blood and may be less sensitive to hypoxia. The study seems to confirm the same. In medicine, it is very difficult to question a given laboratory test as we typically default to trust the machine. It is important for us to consider this when the readings do not match the patient.
This diagnostic accuracy study found that fingertip oximeters sold for home use consistently overestimated oxygen saturation by 0.6-1.5%. Previous studies have already shown this for oximeters used in hospitals, so it is unsurprising that home devices have the same issue.
