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Hypoxic challenge test

Patient information A-Z

A person wearing an oxygen mask and having oxygen levels monitored with a pulse oximeter finger probe.
Lung function test equipment

About the hypoxic challenge test

Why am I having a hypoxic challenge test and what is it?

A hypoxic challenge test assesses whether you need supplementary oxygen when flying. In an aeroplane, the cabin pressure is reduced, meaning the level of oxygen in the air is equivalent to 15% compared to 21% at ground level. This can mean some people require extra oxygen to fly safely.

What does a hypoxic challenge test involve?

At the beginning of the test we will take an arterial blood sample from your wrist. You will then breathe a reduced oxygen mixture of 15%, using a face-mask, to simulate the conditions on a plane. Your blood oxygen levels and heart rate will be monitored for the next 20 minutes. At the end of the test, a second blood sample will be taken while you are still breathing the 15% oxygen.

If your blood oxygen levels decrease during the test, it may be necessary for the physiologist to add extra oxygen to see if your blood oxygen levels return to normal.

About your appointment


  • Please take all medication, including inhalers, as normal.
  • The test will last approximately 90 minutes.

If you cannot attend your appointment

If you need to rearrange your appointment, or no longer need an appointment, please call us on 01223 217065 at the earliest opportunity. Reallocating appointments helps us to reduce waiting times.

What if I am unwell prior to the appointment?

If you are unwell, please call us on 01223 217065 at the earliest opportunity. If you are unwell on the day of the appointment please still call and let us know as this will allow us to rearrange your appointment for a more suitable time.

Who will be present at my appointment?

Cambridge University Hospitals NHS Trust (CUH) is a teaching hospital and so there may be occasions when a student or staff member accompanies your physiologist. We will, however, always seek your permission first.


You will be asked for consent to perform tests during your appointment. You will also have an opportunity to ask questions before you give consent. In the unlikely event there are risks related to the test, these will be discussed with you before the test starts.

Test results

After your appointment, your test results will be sent to your referring consultant, who will then contact you to discuss the results and the way forward.


According to the World Health Organization (WHO), arterial blood tests carry a risk of bleeding or bruising at the puncture site, feeling faint, blood accumulating under the skin, infection at the puncture site and, in rare cases, nerve damage. Your blood test will be performed by a trained practitioner and the risks kept to a minimum.

Contacts/ Further information

If you are unclear about any of the information provided in this leaflet or have any other questions then please do not hesitate to contact the Lung Function Department at Addenbrooke’s Hospital on 01223 217065 or Clinic 2A on 01223 216645.

Our opening hours are Monday to Friday from 08:30 to 16:30.

Further information and support groups

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

Other formats

Help accessing this information in other formats is available. To find out more about the services we provide, please visit our patient information help page (see link below) or telephone 01223 256998.

Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151