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COPD Diagnostic Tests: Pulmonary Function, Spirometry, and More

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Pulse Oximetry

A pulse oximeter is a simple device used to estimate the percent of oxygen in your blood (SpO2). The oximeter can be clipped on your finger or an ear lobe and provides immediate results. Pulse oximetry is not as accurate as getting the oxygen saturation level from an arterial blood gas test. But it is a quick and easy test for getting oxygen levels. Most doctors try to keep oxygen saturations at 88 percent or better. It is normal for saturation values to vary during exercise, sleep and other activities.

The oximeter relies on the fact that hemoglobin that is carrying oxygen is a different color than hemoglobin that is not carrying oxygen. Blood traveling through a vein after it has delivered oxygen to the body is dark red. Blood in an artery that is still carrying oxygen is bright red. By shining a special light through the skin, the oximeter measures how much light is absorbed by the hemoglobin. It then determines what percent of the hemoglobin is carrying oxygen.

Oximetry can be used to help evaluate low oxygen levels in the blood. It can also help in deciding if there is a need for oxygen therapy. However, in patients with severe COPD, an arterial blood gas test is often preferred for making these decisions. An arterial blood gas test is more accurate and gives more information on the PaCO2 and pH values in the body. Pulse oximetry is very useful for measuring oxygen levels while walking, exercising or during sleep. These measurements can provide important information for deciding the earliest need for oxygen therapy. Pulse oximetry can also help determine how well the oxygen therapy is working. However, pulse oximetry can undervalue oxygen levels. This is especially true if the pulse is rapid and harder to gauge.

If you have your own oximeter, talk with your health care provider to decide how to use it correctly. It is not always a good idea to constantly monitor your oxygen levels with every activity you do.  Overuse of an oximeter can lead to unnecessary fear and anxiety.

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