Overnight Pulse Oximetry Test to Evaluate Oxygen Levels

An overnight pulse oximetry test is a commonly used screening test that evaluates blood oxygen levels. Your healthcare provider may recommend one if you are suspected of having a sleep disorder like obstructive sleep apnea. This test is also used to qualify for home oxygen use.

This article explains the overnight pulse oximetry test, what happens when you have one, and how the information is used.

What Is Overnight 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, like sleep apnea.

The test typically involves applying a plastic clip called an oximeter 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 usually 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. Newer devices may adhere directly to the skin and provide similar measurements.

Within the overnight oximeter sensor is a red light. This red light shines through your finger or the surface of your skin.

Often on the other side, or sometimes parallel to the emitting light, is a sensor that can measure your pulse (or 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 that it contains.

Highly oxygenated blood is redder, while blood that is poor in oxygen is bluer. This changes the frequency of the light wavelength that is reflected back to the sensor.

During the Test

Pulse oximetry 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. This may happen recurrently in sleep apnea.

It is also possible for the oxygen levels to be sustained at lower levels. This is especially true if there is underlying lung disease like chronic obstructive pulmonary disease (COPD) or emphysema.

Oxygen desaturations may be associated with increases in your heart rate. These events may suggest the presence of sleep apnea. This is because periodic pauses in your breathing and drops in the oxygen level of your blood lead to a spike of cortisol (stress hormone) that impacts the heart.

Interpreting Results

In general, it is considered abnormal if the oxygen levels fall below:

• 88% in adults
• 90% in children

Levels below 88 percent indicate a condition called hypoxemia. When you have hypoxemia, your oxygen levels can be very low. Generally, desaturations to less than 80% are considered severe.

These drops in blood oxygen levels may require treatment. If the underlying cause is sleep apnea, then CPAP or bilevel therapy may be effective.

However, in the absence of sleep apnea, supplemental oxygen may be needed to resolve the abnormality. This means you may need oxygen delivered via tubing to a nasal cannula from an oxygen concentrator or oxygen tank.

Overnight Oximetry Pros and Cons

Overnight oximeter devices are becoming more widely available to consumers. They can be purchased online or even at pharmacies.

Overnight oximetry is easy and inexpensive, but it is not perfect. Oximeters only provide a limited amount of information. In addition, there are subtleties involved in sleep disorders that may not be detectable.

For example, sleep position and sleep stages may impact the degree of oxygen changes, especially:

• Sleeping on your back
• REM sleep 

Simple devices cannot identify these contributions.

Can Overnight Oximetry Monitors Diagnose Sleep Apnea?

Overnight oximetry alone is not adequate to diagnose sleep apnea and cannot be used for insurance purposes to qualify for treatment such as CPAP.

Nevertheless, overnight oximetry may be useful in identifying some people who warrant further testing. Additional tests may include polysomnography, which records multiple body functions to monitor sleep stages, or more extensive home sleep apnea testing. It can also be helpful to ensure that sleep apnea treatment is effective and that oxygen desaturations that were noted on prior diagnostic testing have resolved.

Summary

Overnight pulse oximetry is a test that can help you and your healthcare provider evaluate your breathing while you sleep. The test can suggest certain sleep disorders like sleep apnea or more serious lung conditions like emphysema.

Overnight pulse oximetry is not perfect, so you will likely need additional tests like polysomnography before your healthcare provider will be able to give you a diagnosis.