Assessing the applicability of the new Global Lung Function Initiative reference values for the diffusing capacity of the lung for carbon monoxide in a large population set

BACKGROUND: The single-breath diffusing capacity of the lung for carbon monoxide (D(LCO)) interpretation needs the comparison of measured values to reference values. In 2017, the Global Lung Function Initiative published new reference values (GLI-2017) for D(LCO), alveolar volume (V(A)) and transfer coefficient of the lung for carbon monoxide (K(CO)). We aimed to assess the applicability of GLI-2017 reference values for D(LCO) on a large population by comparing them to the European Community of Steel and Coal equations of 1993 (ECSC-93) widely used. METHODS: In this retrospective study, spirometric indices, total lung capacity, D(LCO), V(A) and K(CO) were measured in adults classified in 5 groups (controls, asthma, chronic bronchitis, cystic fibrosis, and interstitial lung diseases (ILD)). Statistical analysis comparing the 2 equations sets were stratified by sex. RESULTS: 4180 tests were included. GLI-2017 z-scores of the 3 D(LCO) indices of the controls (n = 150) are nearer to 0 (expected value in a normal population) than ECSC-93 z-scores. All groups combined, in both genders, D(LCO) GLI-2017 z-scores and %predicted are significantly higher than ECSC z-scores and %predicted. In the ILD group, differences between the 2 equation sets depend on the D(LCO) impairment severity: GLI-2017 z-scores are higher than ECSC z-scores in patients with no or “mild” decrease in D(LCO), but are lower in “moderate” or “severe” decrease. CONCLUSION: GLI-2017 reference values for D(LCO) are more suitable to our population and influence the diagnostic criteria and severity definition of several lung diseases.