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TLCO
A TLCO test is a simple breathing test that checks how well your lungs move oxygen from the air into your blood. A TLCO test (also called a DLCO test, transfer factor test or gas transfer test) helps doctors understand how well your lungs are working at the deepest level — where oxygen passes into the bloodstream.
The test is safe and non‑invasive. You breathe in a small amount of harmless test gas, hold your breath for a few seconds, and then breathe out. The machine measures how much of the gas your lungs absorbed, which shows how well gas is transferring across your lung tissue.
A TLCO test is especially useful for people with breathlessness, suspected lung disease, or conditions that affect the lung tissue or blood vessels, such as pulmonary fibrosis, emphysema, or pulmonary hypertension
What happens during a TLCO test?
- Breath in: You breathe in a small amount of test gas (including a tiny, safe amount of carbon monoxide).
- Hold your breath: You hold your breath for about 10 seconds so the gas can move across your lungs.
- Breath out: You breathe out into the machine, which measures how much gas your lungs absorbed.
- Repeat if needed: A few attempts may be done to get the most accurate result.
Friendly technicians guide you through the TLCO test so the process feels calm, simple, and easy to follow.
What is a TLCO test?
A TLCO test measures how well your lungs transfer oxygen from the air into your blood.
Why do I need a TLCO test?
It helps diagnose and monitor lung conditions such as pulmonary fibrosis, emphysema, and pulmonary hypertension.
Does a TLCO test hurt?
No. It is painless and only involves normal breathing and a short breath‑hold.
Is the gas safe?
Yes. The amount of carbon monoxide used is extremely small and harmless.
What does a low TLCO mean?
A low TLCO can mean your lungs are not transferring oxygen well. This may happen in lung diseases, anaemia, or problems with blood flow in the lungs.
What does a high TLCO mean?
A high TLCO can occur in asthma, polycythaemia, or sometimes after bleeding in the lungs.
Do I need to prepare for the TLCO test?
You may be asked to avoid smoking, heavy meals, or certain inhalers before the test, as these can affect the results.
Is the TLCO test suitable for everyone?
It may be harder for people who cannot hold their breath or who have very small lung volumes, but your clinician will advise you.
Is a TLCO test done on its own?
It is often done alongside other lung tests, such as spirometry and lung volumes, to give a full picture of your lung health.
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