What is diffusing capacity of lung for carbon monoxide (DLCO) testing?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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DLCO, also known as the TLCO, is a measurement of the conductance or ease of transfer for CO molecules from alveolar gas to the hemoglobin of the red blood cells in the pulmonary circulation. It often is helpful for evaluating the presence of possible parenchymal lung disease when spirometry and/or lung volume determinations suggest a reduced vital capacity, RV, and/or TLC. It should be noted that different units of measure exist worldwide. In the United States, the test is known as the DLCO and the units of measure are mL/min/mm Hg (traditional unit of measure). In contrast, the test is also known as the TLCO and the units of measure are mmol/min/kPa (International System of Units or SI units). The conversion from SI units (mmol/min/kPa) to traditional (mL/min/mm Hg) can be done by multiplying the SI value by 2.987.

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