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

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.

Prognostic Value of the Six-Second Spirometry in Patients with Chronic Obstructive Pulmonary Disease: A Cohort Study.

BACKGROUND: The six-second spirometry has been proposed as an alternative to diagnose airflow limitation, although its prognostic value in patients with chronic obstructive pulmonary disease (COPD) remains unknown. The purpose of this study was to determine the prognostic value of the postbronchodilator forced expiratory volume in 1 second (FEV1)/forced expiratory volume in 6 seconds (FEV6) ratio and FEV6 in COPD patients. METHODS AND FINDINGS: The study population consisted of 2,614 consecutive stable patients with COPD. The patients were monitored for an average period of 4.3 years regarding mortality, hospitalizations by COPD exacerbations, diagnosis of lung cancer, and annual lung function decline. The overall rate of death was 10.7 (95%CI: 8.7-12.7) per 1000 person-years. In addition to male gender, age and comorbidity, FEV6 (hazard ratio [HR]: 0.981, 95%CI: 0.968-0.003) and FEV1/FEV6 quartiles (lowest quartile (<74% pred.): HR 3.558, 95%CI: 1.752-7.224; and second quartile (74-84% pred.): HR 2.599, 95%CI: 1.215-5.561; versus best quartile (>0.89% pred.)) were independently associated with mortality, whereas FEV1 was not retained in the model. 809 patients (30.9%) had at least one hospital admission due to COPD exacerbation. In addition to sex, age, smoking and comorbidity, FEV1 and FEV1/FEV6 quartiles were independent risk factors of hospitalization. FEV6 was the only spirometric parameter independently related with lung function annual decline, while the FEV6 and FEV1/FEV6 quartiles were independent risk factors for lung cancer. CONCLUSIONS: In a general COPD outpatient population, airflow obstruction assessed by the FEV1/FEV6 is an independent risk factor for both death and hospitalization.