Transfer Test/Diffusing Capacity

This test is used to evaluate the diffusing capacity of the lung and measures how well the lung exchange gases This is an important part of lung testing, because the major function of the lungs is to allow oxygen to "diffuse" or pass into the blood from the lungs, and to allow carbon dioxide to "diffuse" from the blood into the lungs.

Test Duration


Approximately 15 minutes

Test Preparation



You may generally continue with your normal routine. However, there are some points to note to improve comfort and ensure accurate results:

Refrain from smoking for as long as possible before the test

Avoid tight clothing

Avoid a heavy meal 2 hours before the test

Do not drink alcohol for at least 4 hours before the test

Avoid vigorous exercise for a few hours before the test

If you use an inhaler please bring it with you

Follow your doctor's instructions about whether you should avoid use of inhaled breathing medications or other medications before the test.

If it is your first time attending the Respiratory Department for a Lung Function Test do not take the following medication before the test:

Salbutamol (Ventolin, Salamol) or Brycanil for at least 4 hours

Atrovent or Combivent for at least 8 hours

Symbicort, Serevent, Seretide for 12 hours

Spiriva (Tiotropium) for 24 hours.


Please take all other drugs as prescribed.


Test Procedure:

You will be asked to blow out slowly all the air that you possibly can and then inhale a test gas mixture rapidly and completely, reaching your total lung capacity as nearly as possible.

You will be asked to breathe in (inhale) air containing a very small amount of a tracer gas, such as carbon monoxide.

You hold your breath for 10 seconds and after rapidly blow it out (exhale). The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath.

Risks Involved



Diffusion Testing is generally a safe test and there are no significant risks involved. Rarely, the test triggers severe breathing problems.

If you have any of the following please call us to discuss:

  • Unstable angina
  • A recent pneumothorax (air trapped beneath the chest wall)
  • A recent heart attack or stroke
  • Recent eye or abdominal surgery
  • Coughed up blood recently and the cause is not known

Patient Information

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