Lung diffusion testing

Lung diffusion testing measures how well the lungs 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.

How the Test is Performed

You breathe in (inhale) air containing a very small amount of carbon monoxide and a tracer gas, such as methane or helium. You hold your breath for 10 seconds, then rapidly blow it out (exhale). The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath.

How to Prepare for the Test

Before taking this test:

  • Do not eat a heavy meal before the test.
  • Do not smoke for at least 4 to 6 hours before the test.
  • If you use a bronchodilator or other inhaled medicines, ask your doctor whether you can use them before the test.

Why the Test is Performed

The test is used to diagnose certain lung diseases, and to monitor the status of people with established lung disease. Repeatedly measuring the diffusing capacity can help determine whether the disease is improving or getting worse.

Normal Results

Normal test results depend on a person’s:

  • Age
  • Gender
  • Height
  • Haemoglobin (the protein in red blood cells that carries oxygen) level

What Abnormal Results Mean

Abnormal results mean that gases do not move normally across the lung tissues into the blood vessels of the lung. This may be due to lung diseases such as:

  • Emphysema
  • Interstitial fibrosis( scarring of the lung)
  • Pulmonary embolism( Blood clots in the lung)
  • Pulmonary hypertension( high pressure inside the lungs)
  • Sarcoidosis (an inflammatory condition)
  • Lung haemorrhage


If you have any questions or would like to make an appointment to discuss your Sleep or Lung related problem, please fill out the form and submit.