Which pattern on DLCO and A-a gradient is typical of interstitial fibrosis?

Which pattern on DLCO and A-a gradient is typical of interstitial fibrosis?

• A. Decreased DLCO and increased A-a gradient
• B. Increased DLCO and decreased A-a gradient
• C. Normal DLCO and normal A-a gradient
• D. Decreased DLCO and decreased A-a gradient

Answer: (A)

Interstitial fibrosis thickens the alveolar-capillary membrane and reduces the surface area available for gas exchange, so the lungs’ ability to transfer carbon monoxide is diminished, leading to a decreased DLCO. This same process also impairs oxygen transfer from alveoli to blood, which widens the alveolar-arterial (A-a) gradient because arterial oxygen becomes lower than alveolar oxygen, especially with activity when oxygen demand rises. So the typical pattern is a reduced DLCO with an increased A-a gradient.

Interstitial fibrosis thickens the alveolar-capillary membrane and reduces the surface area available for gas exchange, so the lungs’ ability to transfer carbon monoxide is diminished, leading to a decreased DLCO. This same process also impairs oxygen transfer from alveoli to blood, which widens the alveolar-arterial (A-a) gradient because arterial oxygen becomes lower than alveolar oxygen, especially with activity when oxygen demand rises. So the typical pattern is a reduced DLCO with an increased A-a gradient.