Appraisal and extension of the ERS/ATS Interpretative Strategy for Pulmonary Diffusing Capacity.

The ERS/ATS22 interpretative flowchart classifies diffusing capacity (DLco) into 5 scenarios with associated pathophysiology, and has not been tested on large patient groups. We aimed to obtain a more layered DLco interpretation, by interrogating DLco components Kco and VA, and by estimating lung inflation during the DLco test to identify the presence of restriction, which crucially impacts Kco interpretation. By assessing a "low VA" against lung inflation, a novel 9-scenario DLco classification with associated pathophysiology can be obtained. Lung patients from a tertiary center were classified according to the ERS/ATS22 chart and the novel 9-scenario one. Besides a control group of healthy subjects (n=303), disease groups under study were the following : asthma (n=1615), COPD (n=1338), CF (n=108), extrapulmonary restriction (n=122), ILD (n=98), post-COVID (n=193). Except for COPD, the prevalence of "normal DLco" (ERS/ATS22) was generally greater than that of "normal VA and normal Kco" (9-scenario); this discrepancy was most marked in CF (81% vs 56%) and in extrapulmonary restriction (57% vs 37%). With the novel 9-scenario chart, patients from very different diagnostic groups with a "low DLco" due to emphysema, bronchial disease, interstitial damage or incomplete expansion got classified across distinct scenarios, whereas ERS/ATS22 just grouped them together. In conclusion, when "low VA" is evaluated against lung inflation, a differentiation of DLco interpretation can be obtained in various patient groups involving obstruction and/or restriction. This approach can be readily implemented in clinical practice.