Understanding Accuracy, Bias, and Variability in SpO2 Readings

A recent study has raised some questions about differences in pulse oximeter (SpO2) measurements produced by oximeters made by different manufacturers.1 The study compared Nonin pulse oximetry in a home sleep apnea testing (HSAT) device to pulse oximetry in a polysomnograph (PSG). Based on the data collected, authors wrote that “it was not possible to determine which pulse oximeter provided the most accurate determination of overnight arterial blood oxygen saturation.”

So, which pulse oximeter does provide that information? We recommend looking at three factors: measurement bias, motion tolerance, and averaging speed.

averaging speed, motion tolerance, measurement bias

Measurement Bias

The difference between noninvasive pulse oximetry (SpO2) and direct measurement of blood gas (SaO2) is called bias. A recent prospective cohort study was conducted to assess the bias, precision, and accuracy of pulse oximeters used in intensive care units. Pulse oximeters from another leading brand were most accurate at the highest saturation levels; measurement accuracy declined sharply at lower saturations.2

SpO2, Pulse Oximetry, Measurement Bias

Motion Tolerance

Some pulse oximeters provide accurate measurements when the subject is still, but become less consistent and reliable in the presence of motion. Multiple factors can cause motion, from shivering to the involuntary movements of a sleeping subject. In one study, researchers monitored the blood oxygen saturation levels of people recovering from procedural anesthesia, when motion from shivering is common. They took note of failed readings, called dropouts, and their duration.3

SpO2, Pulse Oximetry, Motion Tolerance

Averaging Speed

Nonin PureSAT® pulse oximetry technology utilizes an intelligent, pulse-by-pulse averaging algorithm that is able to
adjust with the patient’s condition for precision accuracy. The PureSAT averaging algorithm automatically adjusts to provide
fast response of 3 seconds or faster(based on pulse rates 60 BPM and greater) for adult, pediatric and infant/neonate —
with no modes to set or adjust. Nonin’s intelligent PureSAT technology provides quick averaging and identifies the true pulse for
patient assessment.

Nonin PureSAT Technology
Clinically proven PureSAT technology provides precise measurements even in the presence of dark skin, motion, low perfusion and other challenging conditions. Nonin pulse oximetry technology is incorporated in polysomnography systems sold worldwide.


1Xu L, Han F, Keenan B, Kneeland-Szanto E, Yan H, Dong X, Chang Y, Zhao L, Zhang X, Li J, Pack A, Kuna S. (2019). Validation of the Nox-T3 Portable Monitor for Diagnosis of Obstructive Sleep Apnea in Chinese Adults. J Clin Sleep Med. 2017 May 15; 13(5): 675–683. doi: 10.5664/jcsm.6582

2Singh AK, Sahi MS, Mahawar B, Rajpurohit S. Comparative Evaluation of Accuracy of Pulse Oximeters and Factors Affecting Their Performance in a Tertiary Intensive Care Unit. J Clin Diagn Res. 2017 Jun; 11(6): OC05–OC08. doi: 10.7860/JCDR/2017/24640.9961

3 Dixon K, Shuler M, Broussard A, Roskosky M. (2017). A Comparison of Wireless Pulse Oximetry Technologies during Sustained Shivering in Post-Operative Patients. J Anesth Clin Res. 8. 10.4172/2155-6148.1000770.