Grading the severity of airways obstruction: new wine in new bottles

Abstract

The objective of this study was to redesign the current grading of obstructive lung disease so that it is clinically relevant and free of biases related to age, height, sex and ethnic group.Spirometric records from 17 880 subjects (50.4% female) from hospitals in Australia and Poland, and 21 191 records (53.0% female) from two epidemiological studies (age range 18-95 years) were analysed. We adopted the American Thoracic Society(ATS)/European Respiratory Society (ERS) criteria for airways obstruction based on an forced expiratory volume in 1 s (FEV1)/(forced) vital capacity ((F)VC) ratio below the fifth percentile and graded the severity of pulmonary function impairment using z-scores for FEV1, which signify how many standard deviations a result is from the mean predicted value.Using the lower limit of normal for FEV1/(F)VC and z-scores for FEV1 of -2, -2.5, -3 and -4 to delineate severity grades of airflow limitation leads to close agreement with ATS/ERS severity classifications and removes age, sex and height related bias.The new classification system is simple, easily memorised and clinically valid. It retains previously established associations with clinical outcomes and avoids biases due to the use of per cent predicted FEV1. Combined with the Global Lung Function prediction equations it provides a worldwide diagnostic standard, free of bias due to age, height, sex and ethnic group. @ERSpublications Using FEV1 z-scores to classify severity of airways obstruction is clinically valid and overcomes bias inherent in % pred

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’

“…<lower limit of normal (LLN)] [1,2]. In practice, once the OVD diagnosis is retained, it is essential to grade its severity into five degrees based on the FEV 1 [1,3]. However, nowadays, there is no clear consensus, neither as to what constitutes a LLN, nor as to how express the FEV 1 .…”

“…Surprisingly, there is a disagreement between the ATS/ERS and the GLI on the way to express the FEV 1 [1,3]. While the ATS/ERS classification is based on the FEV 1 expressed in percentage of the predicted value (%pred) [1], the GLI new classification is based on the FEV 1 Z -scores [3].…”

“…The present Scientific Letter aimed to ascertain how well the GLI criteria to diagnosis the OVD [2] and to grade its severity [3] fit those recommended by the ATS/ERS [1]. …”

“…The OVD was defined according to the ATS/ERS [FEV 1 /FVC < LLN (=local norms value − 1.64 × residual SD) [1]] and the GLI [FEV 1 /FVC Z -score < ‘−1.64’ [2]] criteria. The following two severity classifications were applied: ATS/ERS [1] [based on the FEV 1 %pred [11,12]: mild (>70%), moderate (60–69%), moderately severe (50–59%), severe (35–49%), and very severe (<35%)]; GLI [based on the FEV 1 Z -score [3]: mild (≥−2.0), moderate (−2.5 to −2.0), moderately severe (−3.0 to −2.5), severe (−4.0 to −3.0), and very severe (<−4.0)]. Analyses were carried out using Statistica software (Statistica Kernel version 6; StatSoft, Paris, France).…”

“…The main result of this study was that the diagnosis and the classification of the OVD using the GLI method [2,3] resulted in a change in the frequencies and the severity degrees established by the ATS/ERS recommendations [1]. …”