Diffusing capacity is a measure of how well oxygen and carbon dioxide are transferred (diffused) between the lungs and the blood, and can be a useful test in the diagnosis and to monitor treatment of lung diseases. Diffusing capacity can also be important prior to lung surgery as a predictor of how well the surgery will be tolerated. Diffusing capacity may be reduced in a few ways, and healthcare providers usually use the measure along with other pulmonary function tests to diagnose and determine the severity of either restrictive or obstructive lung diseases.
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Reasons to Perform Lung Diffusion Testing
There are 3 primary reasons why your healthcare provider may order lung diffusion testing. These include:
Meaning of a Low Diffusing Capacity
Oxygen and carbon dioxide both need to pass through a thin layer in the lungs called the alveolar-capillary membrane. This is the layer between the small air sacs in the lung (thealveoli) and the smallest blood vessels that travel through the lungs (capillaries).
How well oxygen that is inhaled can pass (diffuse) from the alveoli into the blood, and how well carbon dioxide can pass from the blood capillaries into the alveoli and be exhaled, depends on how thick this membrane is, and how much surface area is available for the transfer to take place.
Testing Diffusing Capacity
Testing for diffusing capacity is often done along with otherpulmonary function tests. In this test, a mask is placed over your face. During the test, you will take in a deep breath of gas, hold your breath, and then the air that you exhale will be measured.
This test is often referred to as DLCO — which stands for diffusion across the lungs of carbon monoxide.
Causes of Low Diffusing Capacity
There are several conditions that may result in low diffusing capacity. Restrictive lung diseases such as pulmonary fibrosis most often decrease diffusing capacity (DLCO) because of scarring and thickening of the area between the alveoli and capillaries.
Conditions not related directly to lung function can also result in a decreased surface area available between the alveoli and capillaries. For example, a blood clot in an artery in the lungs (pulmonary embolism) may result in carbon monoxide brought into the alveoli being unable to be transferred to the capillaries which the artery supplies.
Diseases Associated With a Low Diffusing Capacity
Understanding a low diffusing capacity requires looking at the differences between obstructive and restrictive lung diseases and how these affect lung function.
Restrictive Lung Diseases Causing Thickening of the Alveolar-Capillary Membrane
Obstructive Lung Diseases and Diseases Causing Less Surface Area in the Lungs
Other Conditions Which Decrease the Surface Area of the Alveoli-Capillary Membrane
How to Increase Lung Capacity Using Breathing Exercises
Causes of High Diffusing Capacity
Rarely, DLCO may instead be high. This may occur withasthma, polycythemia vera (a disease with an elevated hemoglobin level), and congenital diseases that cause blood to be shunted from the left side of the heart to the right side of the heart. With these conditions, however, there are often other signs, symptoms, and testing abnormalities that lead to the diagnosis.
A Word From Verywell
Diffusing capacity is but one test that is used to evaluate lung diseases. Though the test (as well as others) can be confusing, learning about the meaning behind the test can help you better understand your disease.
3 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Institute of Health Medline Plus.Lung diffusion testing.Cleveland Clinic.Gas diffusion study: Results and follow-up.Cleveland Clinic.Gas diffusion study: Test details.Additional ReadingMcCormack, M.Diffusing capacity for carbon monoxide.
3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.National Institute of Health Medline Plus.Lung diffusion testing.Cleveland Clinic.Gas diffusion study: Results and follow-up.Cleveland Clinic.Gas diffusion study: Test details.Additional ReadingMcCormack, M.Diffusing capacity for carbon monoxide.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
National Institute of Health Medline Plus.Lung diffusion testing.Cleveland Clinic.Gas diffusion study: Results and follow-up.Cleveland Clinic.Gas diffusion study: Test details.
National Institute of Health Medline Plus.Lung diffusion testing.
Cleveland Clinic.Gas diffusion study: Results and follow-up.
Cleveland Clinic.Gas diffusion study: Test details.
McCormack, M.Diffusing capacity for carbon monoxide.
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