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The Medical Assistant’s Guide to Pulse Oximetry

August 14, 2026 • Clinical Practice

The Medical Assistant’s Guide to Pulse Oximetry

What is Pulse Oximetry?1,2

 

We all need oxygen to live. Keeping an eye on blood oxygen saturation is critical for the health of the body’s cells, tissues, and organs, allowing them to live, thrive, and perform their proper functions.

Pulse oximetry is a common test that is used by medical professionals to determine the level of oxygen a person has in their bloodstream (also called oxygen saturation). It is a painless, non-invasive way to measure how effectively oxygen is being carried to the extremities, such as arms and legs. This routine test is included when checking the basic vital signs of a patient. A pulse oximetry test involves a small device that clips to either a finger, toe, or earlobe and uses two wavelengths of light to measure the oxygen level that is being carried in the blood. The two wavelengths of light are red light and infrared light. Oxygenated hemoglobin absorbs more infrared light, whereas deoxygenated hemoglobin absorbs more red light. The pulse oximeter recognizes this and determines the level of absorbency, indicating a person’s peripheral oxygen saturation level. The device also uses the detection of light absorption to determine a pulse rate.3

 

How to Operate a Pulse Oximeter2

A pulse oximeter is easy to use and painless for the patient. It consists of a small device that clips to a body part, kind of like a bag clip, if you can picture that! Once applied, the face of the device will show the digital readings of both the oxygen saturation level and the person’s heart rate.

 

You will see the following:

SpO2: 95% (example)

HR: 75 (example)

 

SpO2 stands for:

S=saturaton

p=peripheral (site where it is measured, such as finger)

O2=oxygen

 

Follow these steps when operating a pulse oximeter:

  1. Turn the device on.
  2. Select an appropriate site to apply the device. This can be a finger, toe, or earlobe. You will want to place it where it is warm, there is strong arterial blood flow, and there is relatively thin tissue so the light can be easily transmitted through it.
  3. Tell the patient to relax and remain still.
  4. Wait for a few seconds until the device displays one steady number. Some devices will beep when finished with the reading.
  5. Record the date and time, O2 level, and HR.

 

Interpreting Results

Typical readings from a pulse oximeter are as follows:

SpO2 Levels:

    • 95% - 100%: Normal range in most healthy adults
    • 93% - 94%: Lower than normal, but may be expected depending on the person’s health
    • 90% - 92%: Low, and should be evaluated to determine a need for oxygen supplement
    • Less than 90%: Extremely low, considered to be hypoxemia, and needs to be treated promptly

HR (Heart rate):

    • 60 -100 bpm (beats per minute): Normal resting adult
    • Below 60 bpm: Bradycardia (slow heart rate)
    • Above 100: Tachycardia (fast heart rate)

 

For a complete list of target heart rates per age group, you can visit the American Heart Association webpage at: https://www.heart.org/en/healthy-living/exercise-and-physical-activity/fitness-basics/target-heart-rates

 

Signs and Symptoms of Low Oxygen (Hypoxemia):

Many factors, including chronic health conditions, can contribute to a person having a low oxygen saturation. It is important to interview and observe the patient while obtaining a reading.

 

Typical signs and symptoms are:4

    • A Bluish tint in the face, lips, and nails (cyanosis)
    • Difficulty breathing, shortness of breath, or a cough that is worsening
    • Headache
    • Rapid heart rate (tachycardia)
    • Fatigue/lethargy
    • Confusion
    • Wheezing

 

Inaccurate Readings5

There are many things that can cause an inaccurate reading. Here is a list of things to consider if you are having trouble obtaining results:

    • Faulty device: Damaged, dirty, or one that is not maintained properly
    • Fingernail polish or artificial nails: Can interfere with the light
    • Skin pigmentation: Melanin can inhibit light
    • Smoking or tobacco use: Concern is carbon monoxide, which is produced and present in the blood
    • Altitude: The higher the elevation, the lower the oxygen saturation
    • Temperature of skin: Colder skin will yield lower levels
    • Poor circulation: Decreased peripheral blood flow will render a weak reading
    • Wrong placement of device: Must be placed correctly in order for light to pass through
    • Irregular pulse: This can make it difficult for the device to read accurately
    • Movement of the patient: Creates fluctuations in the light

Always observe the patient. If the numbers don’t line up with what you are observing, double-check the sensor, confirm the placement of the device, remind the patient to be as still as possible, retake the test, and report the results to the provider.

 

What should you do if a patient’s SpO2 or HR is low?

When there is a low SpO2 reading (93% or lower) you should:

  1. Observe the patient first and check for signs of cyanosis, distress, or difficulty breathing. Ask them how they are feeling.
  2. Check the device and its positioning. You should also check to see if the area is cold.
  3. Repeat the test again and compare it with the first reading. Compare the reading also with the patient’s baseline, as they may have a chronic condition causing low oxygen saturation.
  4. Notify the patient’s provider and follow steps to treat according to protocol.
  5. If the patient is starting to decline, shows signs of severe distress, or appears to be unstable in any way, call 911 immediately.

When there is a low (below 60 bpm) or high (above 100 bpm) HR reading, you should:

  1. Observe the patient to see if there are any temporary causes for the reading. For example, an anxious patient might present with a higher HR. A lower HR might present with an altered mental status, dizziness, or weakness. Either way, there might be a clear explanation as to why the value is not normal.
  2. If you sense there is a temporary cause to the abnormal reading, wait a minute before retaking the test and encourage the patient to take a few breaths.
  3. Check the device to see it is positioned correctly.
  4. Repeat the test and compare it with the first set of results and the patient’s baseline.
  5. Obtain the patient’s other vital signs, like BP, temperature, and respiratory rate, if the second test is the same.
  6. Notify the provider and follow the steps according to protocol.
  7. If the patient appears to be having a medical emergency, call 911 immediately.

Obtaining an accurate reading involves more than simply placing a device on the patient’s extremity. It involves observing them, properly interpreting the readings, and following up with an appropriate response. As a medical assistant, by understanding how pulse oximetry works, how to use a pulse oximeter, and how to interpret the readings, you can help ensure an accurate assessment of your patient and do your part to contribute to quality patient care.

 

 

References

  1. Johns Hopkins Medicine. (n.d.). Pulse Oximetry. Retrieved August 6, 2026, from https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/pulse-oximetry
  2. Office of the Commissioner. (2025, March 26). Pulse Oximeter Basics. U.S. Food And Drug Administration. https://www.fda.gov/consumers/consumer-updates/pulse-oximeter-basics
  3. openoximetry.org/. (2022, January 3). How does a pulse oximeter work? - OpenOximetry. OpenOximetry. Retrieved August 6, 2026, from https://openoximetry.org/faq/how-does-a-pulse-oximeter-work/
  4. Hypoxemia. (2026, April 6). Cleveland Clinic. Retrieved August 6, 2026, from https://my.clevelandclinic.org/health/diseases/17727-hypoxemia
  5. Getting an accurate read on pulse oximeters | NIH MedlinePlus Magazine. (n.d.). NIH MedlinePlus Magazine. Retrieved August 6, 2026, from https://magazine.medlineplus.gov/article/getting-an-accurate-read-on-pulse-oximeters

 

 

 

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