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. 2017 Aug 1;196(3):298-305.
doi: 10.1164/rccm.201611-2265OC.

Classification of Airflow Limitation Based on z-Score Underestimates Mortality in Patients with Chronic Obstructive Pulmonary Disease

Elena Tejero  1 , Eva Prats  2 , Raquel Casitas  3   4   5 , Raúl Galera  3   4   5 , Paloma Pardo  1 , Adelaida Gavilán  2 , Elisabet Martínez-Cerón  3   4   5 , Carolina Cubillos-Zapata  4   5 , Luis Del Peso  4   5   6   7 , Francisco García-Río  3   4   5   8
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Free article

Classification of Airflow Limitation Based on z-Score Underestimates Mortality in Patients with Chronic Obstructive Pulmonary Disease

Elena Tejero et al. Am J Respir Crit Care Med. .
Free article

Abstract

Rationale: Global Lung Function Initiative recommends reporting lung function measures as z-score, and a classification of airflow limitation (AL) based on this parameter has recently been proposed.

Objectives: To evaluate the prognostic capacity of the AL classifications based on z-score or percentage predicted of FEV1 in patients with chronic obstructive pulmonary disease (COPD).

Methods: A cohort of 2,614 patients with COPD recruited outside the hospital setting was examined after a mean (± SD) of 57 ± 13 months of follow-up, totaling 10,322 person-years. All-cause mortality was analyzed, evaluating the predictive capacity of several AL staging systems.

Measurements and main results: Based on Global Initiative for Chronic Obstructive Lung Disease guidelines, 461 patients (17.6%) had mild, 1,452 (55.5%) moderate, 590 (22.6%) severe, and 111 (4.2%) very severe AL. According to z-score classification, 66.3% of patients remained with the same severity, whereas 23.7% worsened and 10.0% improved. Unlike other staging systems, patients with severe AL according to z-score had higher mortality than those with very severe AL (increase of risk by 5.2 and 3.9 times compared with mild AL, respectively). The predictive capacity for 5-year survival was slightly higher for FEV1 expressed as percentage of predicted than as z-score (area under the curve: 0.714-0.760 vs. 0.649-0.708, respectively). A severity-dependent relationship between AL grades by z-score and mortality was only detected in patients younger than age 60 years.

Conclusions: In patients with COPD, the AL classification based on z-score predicts worse mortality than those based on percentage of predicted. It is possible that the z-score underestimates AL severity in patients older than 60 years of age with severe functional impairment.

Keywords: airflow limitation; chronic obstructive pulmonary disease; mortality; spirometry; staging.

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