Gas transfer test(KCO)

a Lung function test

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


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

  • What happens during the test? icon plus

    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.
  • How to prepare icon plus

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

    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.

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From complex thoracic surgery to diagnostic tests and procedures, we provide exceptional respiratory and lung care across our network of hospitals, outpatient centres and specialist clinics.

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020 7079 4344
This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
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