TLCO (Gas Transfer Factor – Single Breath)

What a gas-transfer test measures

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 carbon monoxide was taken up by the lungs 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 or vape for at least 1 hour 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

An abnormal result does not identify one condition on its own. Your physician considers it alongside your other results and medical history. Possible causes include lung diseases such as:

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