Which condition is typically associated with a normal DLCO?

• A. Emphysema
• B. Interstitial lung disease
• C. Anemia
• D. Obesity

Answer: (D)

DLCO measures how effectively gas passes from the alveoli into the blood, reflecting alveolar surface area, capillary blood volume, and hemoglobin content. In conditions that shrink the gas-exchanging surface or thicken the membrane—like emphysema (less surface area) or interstitial lung disease (thicker barrier)—the diffusion capacity decreases. Anemia lowers the amount of hemoglobin to carry carbon monoxide, also reducing DLCO. Obesity, however, does not inherently disrupt the alveolar-capillary diffusion process, so DLCO stays normal even though lung volumes and mechanics may be affected. Therefore, obesity is typically associated with a normal DLCO.