Lung Diffusion Testing – Indications, Procedures, Results

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 2 min read

Diffusing capacity; DLCO test

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 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 health care provider whether or not you can use them before the test.

How the Test will Feel

The mouthpiece fits tightly around your mouth. Clips are put on your nose.

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
Hemoglobin (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
Pulmonary embolism
Pulmonary hypertension
Sarcoidosis
Lung hemorrhage
Asthma

Risks

There are no significant risks.

Considerations

Other pulmonary function tests may be done together with this test.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.