What question did this study set out to answer?

The aim is to highlight the importance of both DLCO and KCO in evaluating lung diffusing capacity.

February 14, 2026Open Access

Both DLCO and KCO are vital indices in assessment of diffusing capacity for carbon monoxide by the single-breath method

MYMasafumi YamamotoYokohama City University Medical Center MNMasaharu NishimuraHokkaido Institute of Public Health KSK. ShimizuSapporo University

Key Points

The aim is to highlight the importance of both DLCO and KCO in evaluating lung diffusing capacity.
Measurement of diffusing capacity using the single-breath method
Assessment of DLCO and KCO in relation to various lung conditions
Comparison of DLCO and KCO values in emphysema and fibrosis
Demonstrated a unique change in DLCO and KCO relationship due to emphysema and fibrosis
Indicated that both indices are essential for accurate lung function interpretation
Proposed that KCO is preferable to DLCO/Va to reduce misinterpretation

Abstract

The measurement of diffusing capacity of the lung for carbon monoxide (DLCO) is an invaluable pulmonary function test for assessing gas exchange in the lungs. Typically, the test is conducted via the single-breath method, wherein after maximum inhalation of carbon monoxide and helium simultaneously, the breath is held for 10 s. The test provides the single value of DLCO, and sometimes, the DLCO corrected by alveolar volume (VA) at the measurement. However, DLCO is the product of two independent components in reality-the transfer coefficient for carbon monoxide (KCO) and VA. Conventionally, KCO has often been expressed as DLCO/VA. In this report, we will demonstrate the change in relationship of DLCO with KCO uniquely and characteristically due to emphysema, fibrosis, and their combined disease. Therefore, the assessment of both indices is highly desirable in the precise interpretation of the test. The term "KCO" is preferable to DLCO/VA to avoid misleading.

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