Which description about DLCO testing is correct?

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DLCO testing assesses how well carbon monoxide can diffuse across the alveolar-capillary membrane into the pulmonary capillary blood. Because CO binds rapidly to hemoglobin, the rate of its uptake reflects the surface area and integrity of the diffusion barrier as well as the capillary blood volume. The test typically involves inhaling a small amount of CO with an inert gas, holding the breath briefly, and then exhaling to measure how much CO is taken up, yielding a diffusion capacity value. This is why the description focusing on diffusion capacity for carbon monoxide across the alveolar-capillary membrane is correct. It isn’t about measuring airway resistance, pulmonary venous pressure, or dead space ventilation, which are assessed by other methods.