DLco (or “diffusing capacity”) is a safe and helpful breathing test that measures how well oxygen moves from your lungs into your bloodstream.
DLco testing is typically performed in conjunction with spirometry (and often lung volumes) as part of a complete lung function assessment. Together, these tests give your doctor a clearer and more detailed picture of your lung health.
Why it's Helpful
DLco testing provides information that spirometry alone cannot. It helps your doctor understand how well your lungs are working to transfer oxygen — which can be important when investigating symptoms like:
• Shortness of breath
• Reduced exercise tolerance
• Ongoing cough
• Changes seen on imaging (such as X-ray or CT)
DLco testing can also help assess conditions such as:
• Emphysema
• Pulmonary fibrosis or scarring
• Other lung conditions that affect oxygen transfer
What to Expect
DLco is a gentle test and most people find it very manageable. During the test:
• You’ll be guided to take a big, deep breath in through a mouthpiece.
• You will gently hold your breath for a few seconds.
• Then you’ll breathe out into the mouthpiece.
• The test may be repeated a few times so we can confirm the results are consistent.
Our staff will coach you through each step and let you know exactly what to do as you go.
Lung Function Testing
Quick Prep Checklist
To help your test go smoothly:
- Bring your Alberta Health Care card
- Wear loose, comfortable clothing
- Bring a list of your current medications (inhalers, tablets, injections, etc.)
- You may be asked to hold certain breathing medications (inhalers) before testing
(only if instructed — please follow the directions provided by your doctor or our clinic)
If you are unsure about medication instructions, please contact our clinic prior to your appointment.
FAQ
Yes. DLco testing is very safe. It is non-invasive, does not involve needles, and does not hurt. You are simply breathing through a mouthpiece.
DLco measures how well oxygen moves from your lungs into your bloodstream. It gives your doctor helpful information about how efficiently your lungs are doing their job.
Most patients do not feel short of breath. You will take a big breath in and hold it briefly, but the test is quick and closely guided. If you need a break at any time, just let our staff know.
Holding your breath for a few seconds is an important part of the measurement. It helps the machine accurately calculate how well oxygen moves through your lungs.
DLco testing is usually completed as part of your full lung function appointment. The DLco portion itself typically takes only a few minutes.
Some patients are asked to hold certain breathing medications before testing so results are accurate. If this applies to you, you will be given instructions. If you are unsure, please contact our clinic before your appointment.
Your results are reviewed as part of your overall assessment. A report is then sent to your referring doctor, who will discuss the results and next steps with you.