DLCO measures diffusion capacity for carbon monoxide. Which units are used for this measurement?

DLCO measures diffusion capacity for carbon monoxide. Which units are used for this measurement?

• A. L CO/min/mm Hg
• B. mL CO/min/dL
• C. mL CO/sec/mm Hg
• D. mL CO/min/mm Hg (STPD)

Answer: (D)

DLCO expresses how much carbon monoxide moves from the alveoli into the blood per unit time for each unit of driving pressure. Because it’s a rate that depends on time and a pressure gradient, the standard expression uses milliliters of CO transferred per minute per millimeter of mercury, and it’s adjusted to standard temperature and pressure, dry conditions. This standardization (STPD) ensures values are comparable between labs. Therefore the correct units are mL CO/min/mm Hg (STPD). Per second or per deciliter would not reflect the same diffusion-rate concept, and omitting STPD would reduce cross-lab comparability.

DLCO expresses how much carbon monoxide moves from the alveoli into the blood per unit time for each unit of driving pressure. Because it’s a rate that depends on time and a pressure gradient, the standard expression uses milliliters of CO transferred per minute per millimeter of mercury, and it’s adjusted to standard temperature and pressure, dry conditions. This standardization (STPD) ensures values are comparable between labs. Therefore the correct units are mL CO/min/mm Hg (STPD). Per second or per deciliter would not reflect the same diffusion-rate concept, and omitting STPD would reduce cross-lab comparability.