Table 1.

Characteristics of included studies

Study number	Authors	Publication year	Time frame of patients’ recruitment	Severity of COPD	Parameters under study
1	Fujimoto et al11	2006	September 2002 to September 2004	Moderate, severe	Sex, age, smoking history, onset of symptoms, BMI, α1-antitrypsin, eosinophil counts, daily sputum production, exacerbation rate, hospitalization rate, post-BD FEV1/FVC, post-BD FEV1, TLC, PaO2, PaCO2, response to β2-agonist
2	Martínez-García et al7	2011	January 2004 to December 2006	Moderate, severe	Sex, age, smoking history, onset of symptoms, daily sputum production, daily treatments, dyspnea MRC, exacerbation in previous year, acute antibiotic treatments, acute oral steroid treatments, fibrinogen, albumin, CRP, α1-antitrypsin, post-BD FEV1/FVC, post-BD FEV1, PPM colonization, Pseudomonas aeruginosa isolates, Haemophilus influenzae isolates
3	Bafadhel et al1	2011	Not mentioned	Not mentioned	Sex, age, smoking history, daily sputum production, sputum total cell count, exacerbation in previous year, BMI, SGRQ score, CRQ score, VAS score, ICS dosage, post-BD FEV1/FVC, post-BD FEV1
4	Martínez-García et al13	2013	January 2004 to February 2007	Moderate, severe	Sex, age, smoking history, onset of symptoms, daily sputum production, daily treatments, BMI, dyspnea MRC, exacerbation in previous year, acute antibiotic treatments, acute oral steroid treatments, all-cause mortality, albumin, CRP, α1-antitrypsin, post-BD FEV1/FVC, post-BD FEV1, post-BD FVC, PPM colonization, Pseudomonas aeruginosa isolates, Haemophilus influenzae isolates
5	Tulek et al12	2013	January 2010 to May 2012	Mild, moderate, severe, very severe	Age, smoking history, onset of symptoms, daily sputum production, exacerbation in previous year, albumin, CRP, ESR, post-BD FEV1/FVC, post-BD FE, V1, post-BD FVC
6	Gatheral et al4	2014	January 1998 to September 2008	Not mentioned	Sex, age, onset of symptoms, daily sputum production, post-BD FEV1/FVC, post-BD FEV1, PPM colonization, Pseudomonas aeruginosa isolates, Haemophilus influenzae isolates, respiratory admissions per year, nonrespiratory admissions per year, age at death

Abbreviations: BMI, body mass index; CRP, C-reactive protein; COPD, chronic obstructive pulmonary disease; CRQ, Chronic Respiratory Disease Interviewer-Administered Questionnaire; ESR, erythrocyte sedimentation rate; ICS, inhaled corticosteroid; MRC, Medical Research Council; post-BD FEV₁/FVC, ratio of postbronchodilation forced expiratory volume in 1 second and forced vital capacity; post-BD FEV₁, postbronchodilation forced expiratory volume in 1 second; PPM, potentially pathogenic microorganisms; SGRQ, Saint George’s Research Questionnaire score; TLC, total lung capacity; VAS, visual analog scale.