Which test measures diffusion capacity for carbon monoxide in the lungs?

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Gas diffusion capacity evaluates how well gases move from the air in the alveoli into the bloodstream. Carbon monoxide is used because it binds to hemoglobin very readily, so the rate at which CO is taken up reflects the surface area and thickness of the alveolar-capillary membrane and the pulmonary capillary blood volume. The test that directly measures this diffusion capability is the diffusion capacity for carbon monoxide (DLCO) test. It’s particularly useful for detecting conditions that impair gas transfer, such as fibrosis, edema, or reduced capillary blood volume. Other options measure different things: lung volumes assess the size of the lungs, airway resistance looks at how easily air flows through the airways, and respiratory rate simply indicates breathing frequency without assessing diffusion.