title: Classification of Airflow Limitation Based on z-Score Underestimates Mortality in Patients with Chronic Obstructive Pulmonary Disease.
abstract: 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.
  
  
  
  To evaluate the prognostic capacity of the AL classifications based on z-score or percentage predicted of FEV1in patients with chronic obstructive pulmonary disease (COPD).
  
  
  
  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.
  
  
  
  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 FEV1expressed 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.
  
  
  
  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.
authors.affiliation: 1 Servicio de Urgencias and.
authors.forename: Elena
authors.initials: E
authors.lastname: Tejero
authors.affiliation: 2 Unidad de Neumología, Hospital Universitario de Fuenlabrada, Fuenlabrada, Madrid, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Prats
authors.affiliation: 3 Servicio de Neumología and.|4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Casitas
authors.affiliation: 3 Servicio de Neumología and.|4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: Galera
authors.affiliation: 1 Servicio de Urgencias and.
authors.forename: Paloma
authors.initials: P
authors.lastname: Pardo
authors.affiliation: 2 Unidad de Neumología, Hospital Universitario de Fuenlabrada, Fuenlabrada, Madrid, Spain.
authors.forename: Adelaida
authors.initials: A
authors.lastname: Gavilán
authors.affiliation: 3 Servicio de Neumología and.|4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Martínez-Cerón
authors.affiliation: 4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.
authors.forename: Carolina
authors.initials: C
authors.lastname: Cubillos-Zapata
authors.affiliation: 4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.|6 Departamento de Bioquímica and.|7 Instituto de Investigaciones Biomédicas "Alberto Sols," Madrid, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Del Peso
authors.affiliation: 3 Servicio de Neumología and.|4 Instituto de Investigación Sanitaria, Hospital Universitario La Paz, Madrid, Spain.|5 Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain.|8 Departamento de Medicina, Universidad Autónoma de Madrid, Madrid, Spain; and.
authors.forename: Francisco
authors.initials: F
authors.lastname: García-Río
mesh_terms: D019540:Area Under Curve; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology*; D012131:Respiratory Insufficiency / Q000175:diagnosis / Q000401:mortality* / Q000503:physiopathology*; D012306:Risk; D012720:Severity of Illness Index; D013147:Spirometry; D016019:Survival Analysis
keywords: airflow limitation; chronic obstructive pulmonary disease; mortality; spirometry; staging