Gas transfer test(KCO)


HCA UK uses gas transfer (KCO) to measure how well carbon dioxide and oxygen are exchanged in your lungs

Enquiries & Appointments

Our Gas transfer test(KCO) locations

London Bridge Hospital

London Bridge Hospital

27 Tooley Street SE1 2PR London
The Wellington Hospital

The Wellington Hospital

8A Wellington Place NW8 9LE London

This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.


The primary function of your lungs is the exchange of gases between the air you breathe and your pulmonary circulation. The main gases are:

  • oxygen, which is transferred from the air via your lungs to your tissues, and;
  • carbon dioxide, which is produced as a waste product of breathing and is expelled via your lungs.
  • The gas transfer test measures how efficient your lungs are at exchanging gases. Certain lung diseases affect gas exchange in your lungs. For example, gas transfer will be reduced in emphysema and pulmonary fibrosis. It may also be used to assess your lungs before surgery or to assess how your lungs react when undergoing chemotherapy.

Need to know

During the test you will be seated and your nose will be sealed with a nose clip. You'll be asked to breathe normally into a mouthpiece, followed by a relaxed blow all the way out. You'll then be asked to breathe in as deep and quickly as possible. When your lungs are full, you'll be asked to relax and hold your breath for approximately nine seconds, and then to relax and blow all the way out.

The test involves breathing in a test gas mixture containing a low concentration of helium and carbon monoxide (CO). The gases are not harmful. The test is performed a minimum of two times and you'll be given a minimum of four minutes rest between each test.

The results can be affected by smoking, so if you are a smoker, try not to smoke for 24 hours before your test.

The test tells your consultant how efficient your lungs are at exchanging oxygen from the lungs into the blood. The results will depend on your age, height, gender and ethnicity as well as the level of haemoglobin in your blood. Haemoglobin is the protein in red blood cells that carries oxygen.