[The GLI-2012 reference values for forced spirometry accurately portray the European and French population]

[The FEV1/VC ratio to define bronchial obstruction: Should we use a fixed ratio or the lower limit of normal?]

INTRODUCTION

While the screening of chronic obstructive lung diseases (COPD, asthma, etc.) constitutes a major public health issue in France and worldwide, simple spirometry appears currently as the key to meeting the challenge. Since description of the forced expiratory maneuver by Robert Tiffeneau in 1947, it has been admitted that the FEV1/VC ratio permits diagnosis obstructive pulmonary diseases. However, the diagnostic criteria for this ratio remain uncertain. The long-lasting debate between advocates of a 0.7 "fixed ratio" (FR) of 0.7 and advocates of the "lower limit of normal" (LLN) remains relevant.

STATE OF THE ARTS

In this general review, we describe the respective advantages of the FR and LLN criteria according to the most recently published studies, and characterize the conditions associated with discrepancies between these criteria.

PERSPECTIVES AND CONCLUSIONS

FR and LLN appear not to share similar diagnosis values and the use of both criteria facilitates proposal of an up-to-date interpretation and diagnosis strategy in the context of first-line spirometry, particularly for patients with FEV1/VC ratio in the "grey zone".

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 (DLCO) interpretation needs the comparison of measured values to reference values. In 2017, the Global Lung Function Initiative published new reference values (GLI-2017) for DLCO, alveolar volume (VA) and transfer coefficient of the lung for carbon monoxide (KCO). We aimed to assess the applicability of GLI-2017 reference values for DLCO 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, DLCO, VA and KCO 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 DLCO 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, DLCO 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 DLCO impairment severity: GLI-2017 z-scores are higher than ECSC z-scores in patients with no or "mild" decrease in DLCO, but are lower in "moderate" or "severe" decrease.

CONCLUSION

GLI-2017 reference values for DLCO are more suitable to our population and influence the diagnostic criteria and severity definition of several lung diseases.