Oxygen saturation is a measure of how much oxygen is being carried by the red blood cells in your blood. It is expressed as a percentage, with the abbreviation SpO2. Think of your red blood cells as delivery trucks and oxygen as their cargo. A higher percentage means more of these “trucks” are fully loaded with oxygen to supply your body’s tissues. This measurement provides a snapshot of how well your lungs are taking in oxygen and delivering it to your bloodstream.
Measuring Oxygen Saturation
The most common way to measure oxygen saturation is with a device called a pulse oximeter. This small, clip-like instrument is non-invasive, meaning it does not break the skin. It is placed on a fingertip, but can also be used on an earlobe or a toe. The device works by shining red and infrared light through the tissue and uses the amount of light that passes through to calculate the percentage of oxygen in the blood.
This reading is known as SpO2. While a pulse oximeter provides a quick measurement, a more precise reading, called SaO2, can be obtained through an arterial blood gas (ABG) test. This test requires drawing blood from an artery and is performed in a hospital setting for more detailed analysis. For routine monitoring at home, the SpO2 measurement from a pulse oximeter is the standard method.
Expected Oxygen Saturation Levels
Newborns and Infants
Immediately after birth, it is normal for a newborn’s oxygen saturation to be lower as they adapt to breathing air. Their levels can be as low as the high 80s but should rise to the expected range within the first few hours of life. For infants and young children, a normal SpO2 reading is 97% or higher. Consistent readings below this may prompt medical evaluation for underlying issues, such as congenital heart defects.
Children
As children grow from toddlers into adolescents, their expected oxygen saturation range mirrors that of adults. A healthy child should have an SpO2 level between 95% and 100%. While 95% is often considered the lower limit of normal, consistently higher readings are more common in healthy children.
Adults
For healthy adults, the normal oxygen saturation range is 95% to 100%. Most healthy individuals will have readings in the high 90s. It is important to know your baseline reading, as a significant drop from your normal level can be an early indicator of a health problem. People with chronic conditions like Chronic Obstructive Pulmonary Disease (COPD) may have a lower target range, between 88% and 92%, as determined by their healthcare provider.
Older Adults
The normal oxygen saturation range for older adults is the same as for younger adults, 95% to 100%. However, it is not uncommon for individuals over 70 to have a baseline reading that is slightly lower, around 95%, which can be normal for their age group. This can be due to natural changes in lung function that occur with aging. Any significant deviation from an older adult’s usual reading warrants attention.
Understanding Low Oxygen Levels
When oxygen saturation falls below the normal range, it can lead to a condition called hypoxemia, a low level of oxygen in the blood. If this persists, it can result in hypoxia, where the body’s tissues do not receive enough oxygen. Common symptoms include shortness of breath, rapid breathing, and a feeling of restlessness or confusion.
A more distinct sign of low oxygen is cyanosis, which is a bluish discoloration of the skin, lips, or nail beds. This occurs when SpO2 levels drop to very low levels. The brain may be affected when SpO2 levels fall below 80% to 85%. These symptoms are indicators that the body is struggling and should be taken seriously.
Factors Influencing Accuracy and When to Act
Several factors can interfere with the accuracy of a pulse oximeter reading. Dark-colored nail polish, particularly black, blue, and green, can absorb the light from the device and lead to an incorrect measurement. Cold fingers or poor circulation can also cause a falsely low reading because the device cannot detect a strong pulse. Excessive movement while the device is in use can also affect the results.
It is important to know when to act on a low reading. If you are a healthy individual and your oxygen saturation consistently falls below 95%, you should contact a healthcare provider. If a low reading is accompanied by symptoms such as shortness of breath or confusion, seek medical attention promptly. A pulse oximeter is a useful tool for monitoring, but it does not replace a professional medical diagnosis.