A pulse oximeter is a small, non-invasive device used to estimate blood oxygen saturation (SpO2). It clips onto a finger, shining a light through the skin to determine the percentage of oxygen-bound hemoglobin molecules. People use it at home to monitor respiratory conditions or check oxygen levels. The device provides a quick snapshot of how effectively the lungs supply oxygen to the body’s tissues.
Proper Measurement Technique
Accurate readings require proper preparation. Rest quietly for at least five minutes to ensure a stable baseline heart rate and oxygen consumption. Warm your hands if they are cold, as poor circulation affects the device’s ability to sense blood flow.
Dark or thick material interferes with the oximeter’s light beam. Remove nail polish or artificial nails from the index or middle finger used for the reading. Place the fingertip flatly inside the clip so the sensor’s light passes through the nail bed.
After turning the device on, hold the hand still and below the level of your heart, resting it on a stable surface. Movement disrupts the light signal and causes inaccurate readings. Allow the oximeter to remain in place for at least a full minute, or until the displayed numbers stabilize. Record the highest consistent reading once the number has not changed for at least five seconds.
Understanding the Displayed Values
The pulse oximeter displays two significant values. The first is the SpO2 value, which represents the estimated oxygen saturation level as a percentage. This number reflects how much oxygen-carrying hemoglobin in the blood is saturated with oxygen.
For most healthy individuals at sea level, a normal SpO2 reading falls between 95% and 100%. A reading between 90% and 94% is considered mildly low and warrants closer monitoring. Contact a healthcare provider if your reading is consistently 94% or 93% or remains at this level after being rechecked.
A reading of 92% or less is considered low oxygen saturation (hypoxemia) and requires immediate medical attention. Patients with chronic lung conditions, such as COPD, may have a slightly lower target range recommended by a doctor.
The second value is the Pulse Rate (PR), measured in beats per minute (BPM), which indicates heart rate. A resting heart rate for adults is usually between 60 and 100 BPM, confirming the oximeter is accurately detecting the pulse.
Situations That Affect Accuracy
Several physiological and environmental factors can compromise the accuracy of pulse oximeter readings. Poor peripheral circulation, often caused by cold hands, can lead to falsely low SpO2 measurements. Warming hands before measurement helps mitigate this issue.
Sudden movement, such as shivering, creates “motion artifact” that disrupts light transmission, causing values to fluctuate or become unreliable. Strong ambient light, like direct sunlight or intense overhead lamps, can also interfere with the sensor’s light detection mechanism.
Certain medical conditions or substances affect the reading. Carbon monoxide poisoning causes a falsely high SpO2 because the oximeter cannot distinguish between oxygenated hemoglobin and carboxyhemoglobin. Darker skin pigmentation affects accuracy, sometimes leading to overestimation of the saturation level. A low battery level may also result in unstable measurements.