A sensor, attached to a device called a pulse oximeter, is clipped to your finger or ear, and then directs a beam of light through the tissue. The device is able to monitor oxygen saturation in the blood by measuring the amount of light absorbed by oxygenated hemoglobin (the oxygen-carrying pigment in red blood cells).

Purpose of the Oximetry

  • To monitor oxygen levels in patients at risk for decreased oxygen saturation in the blood (hypoxemia), including those who are undergoing surgery, cardiac stress testing, or pulmonary function tests; people who are heavily sedated, severely injured, or using a mechanical ventilation machine; and individuals undergoing studies in a sleep laboratory.

Who Performs It

  • A doctor, a nurse, or a technician

Special Concerns

  • A variety of factors may interfere with the results, including extreme changes in temperature, movement of the fingers, severe anemia, and fingernail polish.
  • This test should not be performed on patients who have taken light-activated drugs for photo-dynamic therapy.

Before the Oximetry

  • If you wear nail polish, remove it from at least one fingernail.

What You Experience

  • The person performing the test will rub your fingertip or ear to increase blood circulation, and attach the monitoring sensor.
  • The procedure is painless and noninvasive, and takes a few minutes.

Risks and Complications

  • None

After the Oximetry

  • No special aftercare is needed.


  • If your oxygen levels are insufficient, you may be given supplemental oxygen through a face mask or small prongs that fit in the nose. Additional tests, such as arterial blood gases, may be needed to determine the cause.
  • If you are recovering from surgery with general anesthesia, the results of oximetry will help determine when you are ready for discharge.
  • Decreased oxygen levels during sleep studies may indicate sleep apnea.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 25 Jan 2012

Last Modified: 27 Jan 2015