Table 1 Definitions of chronic obstructive pulmonary disease within the different studies

Almagro 2015

COPD was defined as a post-bronchodilator forced expiratory volume in the 1st second (FEV1)/forced vital capacity (FVC) ratio < 0.70.

Berger 2004

COPD was defined by the requirement of chronic bronchodilator therapy or a forced expiratory volume in 1 s < 75% of the predicted value or a room air pO2 < 60 or a pCO2 > 50.

Campo 2013

A patient was considered to have COPD combining different sources of data: i) documented history of hospital admission for COPD; ii) treatment with pharmacologic therapies specific for COPD (e.g., inhaled steroids, inhaled anticholinergics, inhaled β-agonists or theophylline).

Enriquez 2011

COPD was defined as a history or presence of physician-diagnosed COPD. Additionally, the patients were required to be on chronic pharmacologic therapy and/or have an FEV₁ < 75% of predicted value.

Jatene 2016

The presence of COPD was determined clinically by local investigators, based on history, clinical presentation, previous examinations, and medications, recorded as COPD in the case report form at enrollment.

Konecny 2010

Very severe COPD was defined as an FEV 1 /FVC ratio ≤ 70% and an FEV 1 ≤ 30% predicted, severe COPD as an FEV 1/FVC ratio ≤ 70% and an FEV 1 between 30% and 50% predicted, and mild-to-moderate COPD as an FEV 1/FVC ratio ≤ 70 and an FEV 1 > 50% predicted.

Nishiyama 2009

A patient was considered to have COPD if it was listed as a comorbid condition in our database and its diagnosis was confirmed by a simple test called spirometry. Such a diagnosis should be considered in any patient who has symptoms of cough, sputum production, or dyspnea (difficult or labored breathing), and/or a history of exposure to risk factors for the disease. In cases where spirometry is unavailable, the diagnosis of COPD should be made using all available tools. Clinical symptoms and signs such as abnormal shortness of breath and increased forced expiratory time can be used to arrive at the diagnosis.

Selvaraj 2005

The diagnosis of COPD was based on the clinical history or obtained from chart review and recorded as a co-morbidity in the database.

Sung 2013

COPD was defined according to one of the following criteria: (1) Information on COPD status was obtained by reviewing chart record of the need for pharmacologic therapy using bronchodilator agent; (2) Past history of a 1-s forced expiratory volume < 70% of the predicted value (by pulmonary function test); (3) Physical examination (by auscultation) showed expiratory wheezing and further confirmed by blood gas and chest radiograph (i.e., emphysematous change); or (4) Current use of bronchodilators prior to acute myocardial infarction.

Zhang 2012

A diagnosis of COPD should be considered in any patient who has symptoms of cough, sputum production, or dyspnea, and/or a history of exposure to risk factors for the disease. The diagnosis is confirmed by spirometry. The presence of a postbronchodilator FEV1 < 80% of the predicted value in combination with an FEV1/FVC < 70% confirms the presence of airflow limitation that is not fully reversible. Where spirometry is unavailable, the diagnosis of COPD should be made using all available tools.