Over Night Oximetry (Sleep Study)

What is over night oximetry?

“Over night oximetry” is a test designed to assess the level of oxygen in your body when you are asleep.

You will need to use this machine in your own home for two consecutive nights.

Why do I need to have this test?

Your doctor has asked that you have this simple non-invasive procedure to check that you are taking in enough oxygen when you are asleep.

What happens during the test?

An appointment will be arranged for you to collect an over night oximetry machine, which will be loaned to you by the hospital. This is used over night in your own home. The Physiologist will explain the test to you and answer any queries that you may have regarding it. The Physiologist will help you to fill out a questionnaire about your sleeping patterns and you will be shown how to use the oximetry machine. The instructions are also attached to the oximetry machine.

What does the oximetry machine do?

The oximetry machine assesses your blood oxygen levels, your pulse and your breathing when you are asleep. This takes place by attaching a probe to the outside of your ring finger before you go to sleep in bed. The probe should be attached for at least 5 hours. If the site of the probe becomes uncomfortable the ring finger on the other hand can be used. The other end of the probe is attached to the machine.

Important information

  • Patients should not consume any alcohol on the day or night of the test.
  • Patients should not wear nail varnish on the night of the test, as the machine does not work if nail varnish is in place.
  • The machine must be returned to the Lung Function Unit. You will be instructed when to return the machine.

Thank you for your cooperation. This will assist us in obtaining accurate information and enable us to provide you with the most appropriate treatment.

Frequently asked questions

Will I experience any discomfort or side effects?

There is no discomfort or known side effects associated with this test.

When will I be told the results of my test?

You are usually told your results at your next clinic appointment, or a letter may be sent to your GP or the doctor who referred you for the test.

What will happen if I do not want to have this test?

If you do not have this test we will not be able to pass important diagnostic information to the doctors. This may affect the medical treatment that you receive.


ARTP/BTS Guidelines for the measurement of respiratory function (1994) Respiratory Medicine, 88, 165194.

NHS Constitution. Information on your rights and responsibilities. Available at www.nhs.uk/aboutnhs/constitution

If you or the individual you are caring for need support reading this leaflet please ask a member of staff for advice.

How to contact us:

Respiratory Physiology
Gate 12
Level 1
Brunel building
Southmead Hospital
BS10 5NB

0117 414 5400 Monday to Friday, 8am to 6pm


© North Bristol NHS Trust. This edition published April 2021. Review due April 2023. NBT002589

Over Night Oximetry (Sleep Study)