What is the impact of different spirometric criteria on the prevalence of spirometrically defined COPD and its comorbidities? Results from the population-based KORA study.

BACKGROUND: There is an ongoing debate about the appropriate spirometric criterion for airway obstruction to detect COPD. Furthermore, the association of different criteria with comorbidity prevalence and inflammatory biomarkers in advanced age is unclear. MATERIALS AND METHODS: Spirometry was performed in a population-based study (n=2,256) covering an age range of 41-90 years. COPD was spirometrically determined either by a fixed ratio (FR) of <0.7 for forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) or by FEV1/FVC below the lower limit of normal (LLN). Comorbidity prevalences and circulating biomarker levels (C-reactive protein [CRP], interleukin [IL]-6) were compared between subjects with or without COPD by the two criteria using logistic and multiple regression models, adjusting for sex and age. RESULTS: The prevalence of spirometrically defined COPD by FR increased with age from 10% in subjects aged <65 years to 26% in subjects aged ≥75 years. For LLN-defined COPD, it remained below 10% for all age groups. Overall, COPD diagnosis was not associated with specific comorbidities, except for a lower prevalence of obesity in both FR- and LLN-defined cases. Both CRP and IL-6 tended to be higher in cases by both criteria. CONCLUSION: In a population-based cohort of adults up to the age of 90 years, the prevalence of spirometrically defined COPD was higher for the FR criterion than for the LLN criterion. This difference increased with age. Neither prevalences of common comorbidities nor levels of the biomarkers, CRP or IL-6, were conclusively associated with the selection of the COPD criterion. Results have to be considered in light of the predominantly mild cases of airway obstruction in the examined study population.