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Overnight Oximetry Is a Commonly Used Screening Test

Simple Test May Reveal Sleep Apnea or Other Disorders

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Updated May 01, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

If you are suspected of having a sleep disorder, your medical provider may recommend that you undergo overnight oximetry, a commonly used screening test. What happens with this test? How is the information used?

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 enclosing 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.

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.

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. There may also 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. Nevertheless it may be useful in identifying some people who warrant further testing, such as polysomnography.

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