The Impact of Skin Tone on Pulse Oximeter Accuracy
Conditions: Accuracy of Pulse Oximetry Across Skin Pigmentation Levels
Sponsor: Rush University Medical Center

IRB Research Proposal 
 
Study Title: The Impact of Skin Tone on Pulse Oximeter Accuracy  
Document Date: January 20, 2026 
NCT: Not assigned 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Abstract 
Background: Pulse oximeters work by the principle of photo-spectrometry and rely on the 
interaction between light and saturated and unsaturated hemoglobin. Pulse oximeters allow for 
the rapid assessment of oxygen saturation in a non-invasive manner, but accuracy of the oxygen 
saturation is of concern.. Previous studies have called attention to the lack of accuracy in pulse 
oximeter readings when considering darker skinned patient populations. This lack of accuracy is 
often referred to as occult hypoxemia, or hypoxemia occurring when the measured oxygen 
saturation of the pulse oximeter is higher than the arterial oxygen saturation measured by blood 
gas analysis. Previously conducted studies had relied on self-report of skin tone values that are 
subjective and not rigorously define or validated, making it difficult to determine the exact role 
skin tone plays in pulse oximeter readings. The goal of this study is to determine what specific 
role skin tone plays in influencing pulse oximeter accuracy.  
Methods: This will be a prospective cohort study at Rush University Medical Center. Patients 
considered for the study will be adult patients over the age of 18 who have been admitted to the 
ICU, general medicine/surgery wards, or visiting the pulmonary function labs and/or outpatient 
pulmonary services clinics at Rush University Medical Center and have an order for ABG 
analysis.  When the patient is having an arterial blood gas drawn for clinical reasons, two pulse 
oximeters (representing the most common models) will be used to obtain oxygen saturation 
values, and the SpO2 value from the bedside monitor will be recorded as well. Subjective skin 
color samples data will be determined using the Monk scale as a reference and recorded. A 
Konica Minolta CM-700d spectrophotometer will also be used to objectively determine skin 
tone. Data will be uploaded to a secure REDCap server and statistical analysis will be conducted 
using SPSS 22.0 software for windows systems.   

Introduction 
Pulse oximeters are diagnostic tools that, allow for the calculation of oxygen saturation 
values based on the consistent and predictable way light of specific frequencies (660nm and 
940nm) interacts with hemoglobin.1 Pulse oximetry conveniently allows clinicians to 
noninvasively monitor oxygen saturation in real time as an alternative to invasive arterial blood 
gas analysis, which is measured from a sample of arterial blood from an intermittent arterial 
blood draw or from an indwelling arterial catheter.1,2  The significance of pulse oximetry is 
profound, as it is commonly used in virtually every patient care area from outpatient clinics to 
emergency rooms, operating rooms, and intensive care units. 3 
Pulse oximeters obtain readings by measuring the amount of projected light that is 
reflected to the sensor. Blood cells that are desaturated absorb more light from the 660nm light 
source and blood cells that are saturated absorb more light from the 940nm light source. These 
reflected values (the light rays that were not absorbed) are recorded. Using the Beer-Lambert law 
the ratio of the two values is calculated and used to determine the oxygen saturation of the 
blood.1  Due to the optical nature of the device (using light and the readout from the photosensor 
to obtain data) pulse oximeters are susceptible to error if interference exists between the sensor 
and the patient skin.4 Errors in pulse oximetry have been a known issue with pulse oximeter 
results for some time, with articles being published in the early to mid-1990’s reporting on the 
effects of skin pigmentation impacting accurate saturation values.2,5 Clinically, this issue is 
significant as occult hypoxemia could impact clinical decisions and is potentially harmful to 
patients. In 2020, Sjoding et al5 noted that pulse oximeters had an average variance of 3.6% in 
patients with light skin tone and 11.4% average variance in patients with dark skin tone. They 
suggested that the rate of occult hypoxemia is three times higher in black patients than in white 

patients. Similarly, Valbuena et al6 used de-identified data from the Extracorporeal Life Support 
Organization (ELSO) registry to determine if pulse oximetry is less accurate in non-White adult 
patients undergoing extracorporeal membrane oxygenation (ECMO) for respiratory failure. They 
concluded that occult hypoxemia is more prevalent in Black patients when compared to White 
patients about to undergo ECMO for respiratory failure. They also noted that pulse oximetry has 
limitations and racially differential usefulness in evaluating hypoxemia for patients in acute 
respiratory failure. Through spectroscopic analysis of heavily pigmented skin, it was revealed 
that an increase in skin pigmentation resulted in lower transmission of light at a frequency of 
700nm.7 Further, a recent large, observational study of prospectively collected data from 
critically ill adults receiving invasive mechanical ventilation examined 5,557 paired 
measurements of invasively measured SaO2 with a SpO2 measured within 10 minutes and found 
the incidence of hypoxemia was three times greater among Black patients compared with White 
patients, and hyperoxemia (PaO2 > 150 mm Hg) was present twice as often among Black 
patients.8 These data suggest that inaccuracy of pulse oximeters in darker skinned individuals is a 
result of both statistical bias as well as variance.8 As a result of these findings, the potential for 
pigmentation to impact pulse oximeter values warrants further investigation and necessitates 
increased scrutiny of the color data recorded.9 To accurately judge color by visual inspection two 
factors must be present: 1) a calibrated light source that has been rated above 90 CRI (Color 
Rendering Index), and 2) a calibrated reference viewed under the same light source to judge the 
color against.10  
Presently, there is a collective body of literature suggesting that pulse oximetry accuracy 
is impacted by skin color.2,5,7,11 As stated by Okunlola et al there has been a renewed interest in 
pulse oximetry due to the COVID-19 pandemic and the Sjoding paper highlighting the issue.2,5,8 

In fact, Senators Elizabeth Warren, Cory Booker, and Ron Wyden sent a letter to the United 
States Food and Drug Administration (FDA) in 2021 urging them to review the interaction 
between a patient's skin color and the accuracy of pulse oximeters.2 That said, current studies 
evaluating pulse oximetry and skin tone are often methodologically flawed, as race itself is used 
to define patients, and there is often lack of objective data on skin tone available for analysis.  
Okunlola et al3 suggests that using race to define patients with dark skin pigmentation is 
problematic. They propose that standardized, less subjective measures should be used to 
understand the impact of skin tone on pulse oximeter performance.10 Additionally, they suggest 
that objective measures be done at the site of pulse oximeter measurements (e.g., both sides of 
the fingertip).2 In addition, the UCSF hypoxia lab, published their protocol for skin color 
assessment in which they specify the surfaces on the hand best suited for assessment as well as 
additional scales for measuring these findings.12 Thus, the purpose of this study is to assess and 
quantify the discordance between SpO2 and SaO2 values across various skin tones (skin 
pigmentation groups). The secondary aim of this study will be to determine the impact of various 
measures such as age, legal sex, reported race, reported ethnicity, reason for admission,  SOFA 
score, blood pressure, heart rate, and respiratory rate have on pulse SpO2 and SaO2 discordance.  
Experimental Design and Methods 
  
This will be a prospective cohort study at Rush University Medical Center. Patients 
considered for the study will be adult patients over the age of 18 who have been admitted to the 
ICU, general medicine/surgery wards, or visiting the pulmonary function labs and/or outpatient 
pulmonary services clinics at Rush University Medical Center and have an order for ABG 
analysis. Each subject will only participate once in the study. 

For each subject, pulse oximetry saturation values (SpO2) will be recorded at the same 
time as the blood drawn for the arterial blood gas analysis (SaO2). While the patient is having an 
arterial blood gas drawn, for reasons other than this study, two pulse oximeters: Masimo Rad-G 
Pulse Oximeter (Masimo Corporation, Irvine, USA) with an averaging time of 8 seconds, and the 
Medtronic Nellcor Portable SpO2 Monitoring System PM10N (Medtronic, Minneapolis, USA) 
with an averaging time of 7 seconds, will be used to obtain oxygen saturation values. The SpO2 
shown on the bedside monitor (Philips, Cambridge, USA) will be recorded as well. Oxygen 
saturation from the blood sample will be analyzed per institution standard.  
Each pulse oximeter will be placed on the patient’s index finger and ring finger (making 
sure that both pulse oximeters tested are on the same hand) with the patient’s middle finger 
separating the two. To reduce the likelihood of light pollution that might impact the results, the 
pulse oximeter probes will be isolated using gauze or a towel. Pulse oximeter sensors will be 
applied in advance of data collection in accordance with the averaging time of each respective 
device, with the value being recorded at the time of the arterial blood gas being obtained.  
Skin Tone Assessment: Each subject’s skin tone will be determined by using the Monk 
Scale (Harvard University, Cambridge, USA). This chart will be compared to the skin tone on 
the index fingernail, the dorsal surface of the fingernail in between the nail bed and the distal 
interphalangeal joint as well as the palmar surface. To assess skin natural skin tone, we will also 
assess an area of the body that is typically not exposed to sunlight, like the inner upper arm. 
Using a Konica Minolta CM-700d (Konica Minolta, 101 Williams Drive Ramsey, NJ 07446 
USA) with skin analysis software version 1.4, we will also objectively measure skin tone at the 
index fingernail, the dorsal surface of the fingernail in between the nail bed and the distal 

interphalangeal joint as well as the palmar surface. To assess skin natural skin tone, we will also 
evaluate an area of the body that is typically not exposed to sunlight, like the inner upper arm. 
Inclusion criteria: 
1. Adult patients over the age of 18 
2. Patients admitted to an intensive care unit, general medicine/surgery wards, or visiting 
the pulmonary function labs and/or outpatient pulmonary services clinics at Rush 
University Medical Center  
3. Patient has an existing order for an arterial blood gas analysis [arterial line or puncture] 
Exclusion criteria: 
1. Patients with heavy scar tissue on the sensor site  
2. Patients with hand tremors  
3. Opaque nail polish that cannot be removed 
Study outcomes 
The primary study outcome is the discrepancy between SpO2 and SaO2 in patients with 
light and dark skin tone. Skin tone will be considered light for patients with Monk Scale between 
A-G, and dark for patients with Monk scale between H-J. The secondary aim of this study will 
be to determine the impact of various measures such as age, sex assigned at birth, reported race, 
reported ethnicity, reason for admission, SOFA score, blood pressure, heart rate, and respiratory 
rate have on pulse SpO2 and SaO2 discordance.  
Data collection  

 
Data collection will be done by directly obtaining the pulse oximeter saturation data 
while the participant is having a blood gas sample taken. The SaO2 value will be obtained from 
the arterial blood gas that is routinely analyzed by the central lab at Rush University Medical 
Center. Data will be entered into REDCap (Version 11.2.4, Vanderbilt University, Nashville, 
USA) secure database.  
 
Baseline information gathered will include demographic information (age, legal sex, race, 
ethnicity, reason for admission), pulse oximeter saturation data, skin tone assessed via Monk 
scale, SOFA score, blood pressure, heart rate, respiratory rate, oxygen device, FIO2 or oxygen 
flow, perfusion index, stability of SpO2 reading, quality of SpO2 waveform, vasopressor use and 
dose, and ABG source [arterial line or puncture].  
Sample size 
This study is a two-group comparison study designed to compare the discrepancy of SpO2 and 
SaO2 in patients with dark and light skin tone. In the study by Foglia et al,13 the discrepancy of 
SpO2 and SaO2 in patients with dark skin pigment was reported as a mean of 5.4%, a standard 
deviation of 5.1%, while a mean of 3.0%, a standard deviation two of 5.0% for patients with light 
skin pigment. With an effect size of 0.48, the number of participants that will be enrolled in our 
study is 140.14 
Data analysis  
Data will be recorded manually and saved in a secure REDCap (Version 11.2.4, 
Vanderbilt University, Nashville, USA) server. Identifiable data such as medical record number 
and birthdate with be collected, but only deidentified data will be shared outside of the 
immediate Rush research group. . Statistical analysis will be done with SPSS statistics software 

(Version 28.0.1, IBM, Armonk, USA). Nominal variables will be presented as frequency 
distribution. Continuous variables will be presented as a mean with standard deviation or as 
median with interquartile ranges, based on normality. Bland-Altman analysis will be performed 
to measure the agreement between the SaO2 values and the SpO2 values. The SaO2 and SpO2 
values between two study groups (light versus dark) will be analyzed with a T-test or the Mann 
Whitney test, based on normality. SaO2 and SpO2 values within a subject will be analyzed using 
paired T-test or Wilcoxon sign rank, based on normality. The dichotomous variables will be 
analyzed using chi square and fisher exact tests, as needed.  Reported p-values will be two-sided 
and p-value < 0.05 will be considered significant.  
Recruitment and informed consent process   
Upon notification of an arterial blood gas order, we will obtain consent from the patient if they 
have the capacity to do so (fully awake, oriented). If not, we will attempt to seek consent from a 
legally authorized representative (LAR). For those without the capacity to consent and for whom 
an LAR is unavailable, the study procedures will be performed and we will seek consent to use 
the data when the patient regains the capacity to consent. If the individual expires or does not 
regain the capacity to consent, the data will still be used. 
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