Pulse oximetry is a noninvasive test that measures the oxygen saturation level of your blood.
It can rapidly detect even small changes in oxygen levels. These levels show how efficiently blood is carrying oxygen to the extremities furthest from your heart, including your arms and legs.
The pulse oximeter is a small, clip-like device. It attaches to a body part, most commonly to a finger.
Medical professionals often use them in critical care settings like emergency rooms or hospitals. Some doctors, such as pulmonologists, may use them in office settings. You can even use one at home.
The purpose of pulse oximetry is to see if your blood is well oxygenated.
Medical professionals may use pulse oximeters to monitor the health of people with conditions that affect blood oxygen levels, especially while they’re in the hospital.
These can include:
- chronic obstructive pulmonary disease (COPD)
- lung cancer
- heart attack or heart failure
- congenital heart disease
Doctors use pulse oximetry for a number of different reasons, including:
- to assess how well a new lung medication is working
- to evaluate whether someone needs help breathing
- to evaluate how helpful a ventilator is
- to monitor oxygen levels during or after surgical procedures that require sedation
- to determine whether someone needs supplemental oxygen therapy
- to determine how effective supplemental oxygen therapy is, especially when treatment is new
- to assess someone’s ability to tolerate increased physical activity
- to evaluate whether someone momentarily stops breathing while sleeping — like in cases of sleep apnea — during a sleep study
Pulse oximetry may be useful in both inpatient and outpatient settings. In some cases, your doctor may recommend that you have a pulse oximeter for home use.
To take a reading with a pulse oximeter, you will:
- Remove any jewelry or fingernail polish on your finger if measuring from this location.
- Make sure your hand is warm, relaxed, and below heart level if attaching the device here.
- Place the device on your finger, earlobe, or toe.
- Keep the device on for as long as needed to monitor your pulse and oxygen saturation.
- Remove the device once the test is over.
In pulse oximetry, small beams of light pass through the blood in your finger, measuring the amount of oxygen. According to the British Lung Foundation, pulse oximeters do this by measuring changes in light absorption in oxygenated or deoxygenated blood. This is a painless process.
The pulse oximeter will be able to tell you your oxygen saturation levels along with your heart rate.
Pulse oximetry tests are an estimation of blood oxygen levels, but they’re typically precise. This is especially true when using high quality equipment found in most medical offices or hospital settings. With this equipment, medical professionals can carry out the tests accurately.
Having an oxygen saturation temporarily below this level may not cause damage. But repeated or consistent instances of lowered oxygen saturation levels may be damaging.
An oxygen saturation level of 95 percent is considered typical for most healthy people. A level of 92 percent or lower can indicate potential hypoxemia, which is a seriously low level of oxygen in the blood.
Various factors can affect readings, including a person’s skin tone.
A 2020 report compared the accuracy of pulse oximetry tests and blood gas measurements in detecting hypoxemia in Black and white patients.
Researchers found that among Black patients, there were three times as many cases of pulse oximetry tests failing to detect occult hypoxemia when blood gas measurements did so.
Tests like these were developed without considering a diversity of skin tones. The authors concluded that more research is needed to understand and correct this racial bias.
Once the test is over, your doctor will have the readings available immediately. This will help them determine if other testing or treatment is necessary.
If you’re evaluating how successful your oxygen supplementation therapy is, for example, a reading that’s still on the low side might indicate the need for more oxygen.
Your doctor will be able to tell you what the next steps are. If you’re using pulse oximetry at home, they’ll let you know how often to take your readings and what to do if they go above or below certain levels.
Pulse oximetry is a quick, noninvasive, and completely painless test. It comes with no risks, aside from potential skin irritation from the adhesive used in some types of probes.
However, it’s not as accurate as clinical blood gas measurements, especially for people with darker skin tones.