Overnight Oximetry Used for Screening Oxygen Levels

Simple Test May Reveal Sleep Apnea or Other Disorders

CPAP machines often have a ramp feature to allow the pressure to be lowered
CPAP machines often have a ramp feature to allow the pressure to be lowered. nicolesy/Getty Images

If you are suspected of having a sleep disorder like obstructive sleep apnea, your medical provider may recommend that you undergo overnight pulse oximetry, a commonly used screening test that evaluates blood oxygen levels. What happens with this test? How is the information used? Learn about oximetry and how it might be helpful to evaluate your breathing in sleep.

What Is Pulse Oximetry?

Overnight oximetry is a simple test that can easily be done at home.

It provides basic information that may be useful in initially evaluating whether you have one of the more common sleep disorders, sleep apnea.

The test involves applying a plastic clip over the end of your finger. Imagine a large clothespin or plastic sleeve that encloses your fingertip. This clip may be held in place with a piece of tape, but it is not painful to have on and it can be removed easily. It is connected via a cable to a small box that records the data overnight. If you use continuous positive airway pressure (CPAP), it can be connected to this device to record the data.

Within the overnight oximeter clip is a red light. This red light shines through your finger. On the other side is a sensor that can measure your heart rate and the oxygen content of your blood. The latter is determined by the color of your blood, which will vary with the amount of oxygen. Highly oxygenated blood is more red, while blood that is poor in oxygen is more blue.

How Can Oximetry Evaluate Oxygen Levels and Identify Sleep Apnea?

These data are recorded continuously over the course of the night and will result in a graph. Your medical provider will be able to review it and determine if there are abnormal drops in your oxygen levels called desaturations. In general, it is considered abnormal if the oxygen levels fall below 88 to 90 percent.

This may occur recurrently in sleep apnea. It is also possible for the oxygen levels to be sustained at lower levels, especially in the setting of underlying lung disease. With the oxygen desaturations, there may be associated increases in your heart rate. These events may suggest the presence of sleep apnea because it involves periodic pauses in your breathing and drops in the oxygen level of your blood.

This screening test is easy and inexpensive, but it is not perfect. It only provides a limited amount of information. In addition, there are subtleties involved in sleep disorders that it may not be able to detect. It is not adequate to diagnose sleep apnea and cannot be used for insurance purposes to qualify for treatment such as CPAP. Nevertheless it may be useful in identifying some people who warrant further testing, such as polysomnography or more extensive home sleep testing. It can also be helpful to ensure that sleep apnea treatment is effective.

If you are concerned that your oxygen levels may be abnormal during sleep, speak with your doctor about the need for further testing and treatment. When oxygen levels are low without the occurrence of sleep apnea, oxygen supplementation with a concentrator may help you to sleep and feel better.

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