A pulse oximeter is a device that measures your pulse rate (or heart rate) and the percentage of oxygen in your blood, showing digital readings for both in a matter of seconds. Pulse oximetry is a quick and painless indicator as to how well your body is working to move the oxygen from your heart to your extremities.
Oxygen is attached to hemoglobin, an iron-rich protein in red blood cells. Pulse oximetry measures the percent of hemoglobin saturated by oxygen, which is called oxygen saturation and is expressed as a percentage. If all the binding sites on the hemoglobin molecule have oxygen, the hemoglobin is 100% saturated.
How Does a Pulse Oximeter Work?
When you insert your fingertip into a pulse oximeter, it uses two non-invasive LED lights—one red to measure deoxygenated blood and the other infrared to measure oxygenated blood. To calculate the oxygen saturation percentage, a photodetector reads the light absorption from these two beams of differing wavelengths.
Typically, an oxygen saturation level is considered normal between 95% and 100%. If it’s lower than 90%, one should seek immediate medical attention.
The FDA notes that these readings should be considered estimates of blood saturation and more accurate measurements can be provided by a blood test.