The most common way to measure oxygen levels in flowing blood is to use pulse oximetry tests. By attaching a probe to the fingertip or earlobe, an infrared light can tell the difference between blood cells that are filled with hemoglobin and blood which is low in oxygen content. This diagnostic test is used to discover conditions like sleep apnea as well as various heart and lung conditions by allowing physicians and technicians determine a percentage of oxygen saturation. It also is also used to monitor blood-oxygen levels during surgery. Other ways to measure oxygen include intracardiac oximetry and instruments that can measure oxygen in blood samples outside the body.
Pulse oximetry tests use a device with a infrared light that shines into capillaries. The light reflected by blood with more oxygen appears different from light reflected from oxygen-deprived blood. Oxygenation between and during pulses is measured and the information is processed and sent to a computer, where physicians can read a graph showing the percentage of oxygen in the blood. Pulse oxymetry is a non-invasive test often done in a lab to diagnose sleep apnea, but can be used to discover and diagnose conditions such as heart attacks, anemia, and asthma.
If oxygen levels need to be measured in blood deeper in the body, then intracardiac oxymetry is performed. Surgeons insert a catheter with a probe inside it that senses the oxygen content of the blood along the way. A fiber optic light is sometimes used, and the device can monitor blood within different parts of the heart to diagnose conditions. The instrument can also incorporate sensors to detect pressure levels in the heart and blood vessels.
There are also oximetry tests that are used on blood outside the body. Samples of blood are monitored in a blood gas analyzer, which can also measure how acidic blood is, the level of electrolytes present, or how much glucose or lactate exists. Such an analyzer is often used to monitor the health of premature infants, and has been found to be a vital tool in assessing their condition quickly.
The different types of oximetry tests are found in intensive care units of hospitals and in medical facilities such as overnight test centers for sleep apnea. Equipment for testing blood-oxygen levels is also available for use at a patient’s home. Variations in oxygen levels in the blood can be an indication of many different health conditions, therefore oximetry tests are often followed by other tests for diagnostic purposes.