Which condition is typically associated with reduced DLCO?

• A. Emphysema
• B. Obesity
• C. Anemia
• D. Deconditioning

Answer: (A)

DLCO shows how effectively gases move from the lung airways into the blood. It depends on the surface area available for diffusion, the volume of blood in the pulmonary capillaries, and the thickness of the alveolar-capillary membrane. Emphysema destroys alveolar walls and reduces the capillary bed, cutting the surface area for diffusion and lowering DLCO.

Obesity mainly affects lung mechanics and volumes rather than the diffusion surface, so DLCO is usually not markedly reduced. Anemia lowers the amount of hemoglobin available to bind carbon monoxide during the test, which can make DLCO appear reduced, though labs often adjust for hemoglobin; this reflects less Hb carrying capacity rather than a problem with the diffusion barrier. Deconditioning does not directly impair the alveolar-capillary diffusion process.