How Do Pulse Oximeters Work?

A pulse oximeter is a small, lightweight device that clips to the end of your finger to measure the amount of oxygen in your blood as well as your pulse rate. If you’ve ever spent time at the hospital, you’ve probably worn one of these. Your doctor might also have put one on your finger during a routine physical.

Pulse oximeters are important tools for understanding an individual’s current condition and noticing signs of any underlying issues. That’s because your blood’s oxygen level depends on how well your heart and lungs are working. Therefore, the readings from a pulse oximeter can reflect the relative health of your pulmonary and cardiovascular system.

But you still might be wondering whether or not you should invest in one to monitor your health. Keep reading to learn how pulse oximeters work and why you may need one.

Pulse oximeters use two LEDs (light-emitting diodes) on one side of the clip. One diode emits red light and one emits infrared light. The light from each diode goes on and off, alternating back and forth between the two types of light about thirty times every second. Then, these wavelengths of light are directed through your finger before hitting a sensor on the other side of the clip. This sensor can tell how much light was absorbed by your finger by reading how much light is making it through.

Because blood absorbs red and infrared light differently at different oxygenation levels, the absorption level corresponds with an oxygenation level. Oxygenated hemoglobin (red blood cells) will absorb more infrared light and non-oxygenated will absorb more red light.See Disclosure ¹ So, the pulse oximeter will convert the sensor reading into the corresponding oxygen saturation level.

At the same time, the light/sensor system can also measure fluctuations in blood volume, which allows you to see your pulse rate (also known as your heart rate).

Ninety-five percent of prescription FDA-approved pulse oximeters give results within 4% to 6% of arterial blood gas levels. And sixty-six percent are within 2% to 3%.See Disclosure ² However, certain circumstances and traits can interfere with accuracy. When taking a reading, remember to follow all manufacturer instructions, make sure your hand is warm and relaxed, sit still and wait until the reading stops shifting.

Consider factors, like nail polish, that can affect readings. Skin color also affects the accuracy of readings. Generally, the difference is not considerable at healthy blood oxygen levels, but hypoxemia (the medical term for a below-normal level of oxygen in your blood) can go undetected more easily in individuals with darker skin.See Disclosure ³

If you use a pulse oximeter at home and you do not get a prescription-based health monitoring device, your machine will not need to pass FDA review. Although, it’s worth noting that statistics about accuracy are not as available for at-home, over-the-counter devices. However, every pulse oximeter can give you worthwhile feedback on whether your oxygenation level is going down or staying at a healthy setting.

Even if the exact number is off by a percentage point or two, tracking ups and downs in blood oxygenation is important, especially if you have respiratory issues or are concerned about the effects of COVID-19. Signs of low blood oxygen levels can include shortness of breath, racing pulse and tightness in the chest. But not everyone will demonstrate these symptoms, which is why having a pulse oximeter helps.

Healthy blood oxygenation levels are between 95% and 100%. If you get a reading below 92%, contact your healthcare provider. If your reading is 88% or lower, you need to head to the emergency room.

If you have a chronic condition, such as COPD, heart disease, or sleep apnea, or you are concerned about the adverse effects of COVID-19, you should have a pulse oximeter at home as part of your health and wellness regimen. This tool can also help your doctor track your condition to see how well treatments are working, and it can help you recognize a possible emergency.

To make sure you don’t overtax your body, there are also smartwatches that can check your oxygenation and pulse rate while working out. If you’re concerned about how snoring might affect your breathing and general sleep health, use a pulse oximeter when you wake up in the morning or in the middle of the night.

You could also explore sleep technology that tracks your breathing and sleep cycles throughout the night for a deeper level of insight. These devices, along with pulse oximeters, can make all the difference between overlooking a serious problem or condition and recognizing when action must be taken to improve your health.

1. Lujan, Heidi L. and DiCarlo, Stephen E. “’Seeing Red’ Reflects Hemoglobin’s Saturation State: A Discovery-Based Activity for Understanding the Science of Pulse Oximetry.” Advances in Physiology Education, American Physiological Society. July 28, 2022. https://journals.physiology.org/doi/full/10.1152/advan.00093.2022.

2. “Pulse Oximeter Accuracy and Limitations: FDA Safety Communication.” Center for Devices and Radiological Health, U.S. Food and Drug Administration. February 19, 2021. https://www.fda.gov/medical-devices/safety-communications/pulse-oximeter-accuracy-and-limitations-fda-safety-communication.

3. Bilderback, Pete. “Brown Ph.D. Student Working to Correct Skin Color Bias in Pulse Oximeters.” News from Brown, Brown University, April 7, 2022. https://www.brown.edu/news/2022-04-07/pulseox#:~:text=%E2%80%9CIt%20has%20also%20been%20found,for%20people%20with%20dark%20skin.