Filho FSL, et al. - Prevalence of immunoglobulin G (IgG) subclass deficiencies and their association with exacerbations and hospitalizations among chronic obstructive pulmonary disease (COPD) patients were determined herein. One or more IgG subclass deficiencies were detected in approximately 1 in 5 COPD patients. Reduced IgG subclass levels were identified as independent risk factors for both COPD exacerbations (IgG1 and IgG2) and hospitalizations (IgG2).