Defining and grading an obstructive ventilatory defect (OVD): ‘FEV₁/FVC lower limit of normal (LLN) vs. Z-score’ and ‘FEV₁ percentage predicted (%pred) vs. Z-score’

ABSTRACT

An obstructive ventilatory defect (OVD) is defined by a low forced expiratory volume/‘forced/slow’ vital capacity (FEV₁/FVC) (e.g. <lower limit of normal (LLN)). However, the LLN can be estimated either by the 90% confidence interval (or the 90th percentile) (American Thoracic and the European Respiratory Societies (ATS/ERS) method) or by the Z-score (global lung initiative (GLI) method). In 2014, a new alternative classification (GLI classification) for grading the OVD severity was proposed to replace the 2005-ATS/ERS one. The aims of the present study were to determine, according to the two methods (GLI vs. ATS/ERS), the frequency of participants having an OVD; and to compare the two classifications (GLI vs. ATS/ERS) of OVD severity. This was a prospective study including 1000 participants (mean age = 41 ± 10 years). The OVD was defined according to the ATS/ERS [FEV₁/FVC < LLN (=local norms value − 1.64 × residual standard deviation)] and GLI (FEV₁/FVC Z-score < −1.64) criteria. The following OVD classifications severity were applied: ATS/ERS (FEV₁%pred): mild (>70%), moderate (60–69%), moderately severe (50–59%), severe (35–49%), and very severe (<35%) and GLI (FEV₁ Z-score): mild (≥ −2.0), moderate (−2.0 to −2.5), moderately severe (−2.5 to −3.0), severe (−3.0 to −4.0), and very severe (<−4.0). The frequencies of OVD were 14.4% (ATS/ERS method) and 10.5% (GLI method) (p < 0.05). Among the 103 participants having an OVD according to the two methods, the severity classification was mild (34.95% vs. 37.86%, p < 0.05), moderate (25.24% vs. 18.45%, p < 0.05), moderately severe (23.30% vs. 15.53%, p = 0.144), severe (9.71% vs. 20.39%, p < 0.05), and very severe (6.80% vs. 7.77%, p = 0.785), respectively for the ATS/ERS and GLI classifications. The two OVD definitions were not exchangeable. Moreover, the two grading severity systems misclassified the OVD grades.

KEYWORDS:

• Bronchial obstruction
• diagnosis
• interpretation
• international guidelines

Acknowledgments

Authors wish to express their sincere gratitude to the following five Pulmonologists from Sousse, Tunisia: Halima Ben Salem, Mohamed Moez Ben Sayah, Mohamed Salah Tlili, Souhail Slama and Mohamed Ben Saad.

Authors’ contributions

RK conceived the study, participated in its design, performed the statistical analysis, and helped to draft the manuscript.

IG conceived the study, participated in its design and helped to draft the manuscript.

SR conceived the study, participated in its design and helped to draft the manuscript

HBS conceived the study, participated in its design, performed the statistical analysis, helped to draft the manuscript and coordinated the study.

All authors read and approved the final manuscript.

Disclosure statement

HBS reports personal fees from AstraZeneca, Boehringer Ingelheim, INPHA-MEDIS and Chiesi. The remaining authors declare that they have no conflicts of interest concerning this article.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.