Once primarily confined to hospitals and intensive care units, the pulse oximeter became a widely recognized household device during the COVID-19 pandemic. As respiratory complications emerged as a defining feature of the disease, monitoring blood oxygen levels at home became crucial for early detection of deterioration. This shift brought attention not only to its clinical utility but also to its limitations, accuracy concerns, and regulatory oversight.
A pulse oximeter is a non-invasive device used to measure peripheral oxygen saturation (SpO₂) and pulse rate. It is commonly clipped onto a fingertip, though it can also be used on the earlobe or toe, especially in newborns.
Its primary purpose is to estimate how well oxygen is being transported in the blood, helping clinicians and patients monitor respiratory and cardiovascular status.
Pulse oximeters operate on the principle of spectrophotometry and photoplethysmography.
The device uses light-emitting diodes (LEDs) to project two specific wavelengths of light, typically red and infrared, from one side of the device through the patient’s skin and underlying tissues. As this light passes through the pulsating arterial blood, it is partially absorbed by hemoglobin depending on its oxygenation state. Oxygenated (bound) and deoxygenated hemoglobin absorb these wavelengths differently.
A photodetector positioned on the opposite side of the device captures the transmitted light, and the variations in absorption during each pulse are analyzed to estimate oxygen saturation levels.
This method allows continuous, real-time monitoring without the need for blood sampling.
The development of pulse oximetry dates back to the 1970s, with significant advancements in Japan and later widespread adoption in clinical settings globally, especially U.S.
It spans more than a century, evolving from early discoveries about hemoglobin in the 19th century to the advanced, non-invasive devices used today. Scientists such as Karl Matthes, Glenn Millikan, and Takuo Aoyagi contributed key breakthroughs, ranging from the first light-based “blood oximeters” to portable ear devices and, eventually, pulse-based measurement techniques.
Aoyagi’s innovation in the 1970s, which used arterial pulsations to estimate oxygen saturation, laid the foundation for modern pulse oximeters. With advancements in electronics and sensor technology through the 1980s and beyond, these devices became smaller, more accurate, and widely accessible in both clinical and home settings.
Pulse oximeters are used across a range of settings:
Monitoring patients with respiratory conditions such as chronic obstructive pulmonary disease and asthma
Assessing oxygenation during surgeries and anesthesia
Monitoring critically ill patients in ICUs
Evaluating patients with COVID-19
Home monitoring for individuals with chronic illnesses
Pulse oximetry offers several benefits:
Non-invasive and painless
Provides immediate results
Portable and easy to use
Enables early detection of hypoxemia (low blood oxygen levels)
Useful in both clinical and home settings
Under ideal conditions, medical-grade pulse oximeters typically have an accuracy range of ±2–3% compared to arterial blood gas measurements. However, real-world conditions and user-related factors can influence this accuracy.
Despite its utility, pulse oximetry has known limitations:
It provides an estimate, not a direct measurement of arterial oxygen levels
Cannot detect carbon dioxide levels or ventilation status
Accuracy may decline in poor perfusion states (e.g., shock, hypothermia, high melanin skin, in case of nail extensions)
Consumer-grade devices may vary in reliability
Several factors can influence the accuracy of pulse oximeter readings, including motion during measurement, the presence of nail polish or artificial nails, poor peripheral circulation, interference from ambient light, and variations in skin thickness (callouses) or temperature. In addition, recent research has highlighted concerns regarding measurement bias related to skin tone. Pulse oximeters may overestimate oxygen saturation levels in individuals with darker skin, as higher melanin levels can affect light absorption. This can potentially mask hypoxemia and has raised important concerns about diagnostic disparities and patient safety in black individuals.
In the United States, pulse oximeters are regulated by the U.S. Food and Drug Administration as medical devices.
Manufacturers must submit 510(k) premarket notifications demonstrating safety and effectiveness.
Clinical validation studies are required, including testing across different skin tones.
The FDA continues to review performance standards, particularly in light of concerns regarding racial bias in readings.
Pulse oximeters have transformed from specialized clinical tools into widely used monitoring devices, especially since the COVID-19 pandemic. While they provide valuable, non-invasive insights into oxygen saturation, their limitations, including potential inaccuracies in certain populations highlight the need for careful interpretation and continued regulatory oversight.
References
U.S. Food and Drug Administration. Pulse Oximeter Basics. Accessed April 2026.
Jubran, Amal. “Pulse Oximetry.” In StatPearls. Treasure Island (FL): StatPearls Publishing, 2023. Accessed April 2026.
Sinex, J. E. “Pulse Oximetry: Principles and Limitations.” American Journal of Emergency Medicine 17, no. 1 (1999): 59–66.
