What test is used to measure the diffusion capacity of the lungs?

The test used to measure the diffusion capacity of the lungs is the DLCO, which assesses how well oxygen and carbon dioxide are transferred from the alveoli into the bloodstream. This test specifically measures the ability of gases to diffuse across the alveolar-capillary membrane, using carbon monoxide as a tracer gas because it is highly soluble and binds to hemoglobin in red blood cells.

A reduced DLCO value can indicate various pulmonary conditions, including emphysema, pulmonary fibrosis, and interstitial lung disease, highlighting its usefulness in diagnosing and assessing the severity of these disorders. This makes DLCO a critical tool in evaluating lung function and overall respiratory health.

Other tests mentioned, like FVC, PEFR, and RV, do not specifically measure diffusion capacity. FVC assesses the maximum volume of air that can be forcefully exhaled, PEFR measures the maximum flow rate during exhalation, and RV reflects the volume of air remaining in the lungs after maximum exhalation. While these tests provide valuable information about lung volumes and airflow, they do not directly evaluate how gases move across the alveolar membranes, which is the primary function of the DLCO test.