Association of fat-free mass index measured by bioelectrical impedance analysis with disease severity in stable COPD: a cross-sectional study

Background Malnutrition and skeletal muscle loss are common extrapulmonary manifestations of chronic obstructive pulmonary disease (COPD) and contribute to increased morbidity and mortality. Fat-free mass index (FFMI) is a sensitive marker of muscle depletion and nutritional status in patients with COPD. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) ABE assessment classifies patients according to symptom burden and exacerbation history. This study aimed to evaluate the association of FFMI with COPD severity and exercise capacity and to assess its ability to discriminate patients classified as GOLD group E. Methods This single-center cross-sectional study included 90 clinically stable COPD patients. FFMI was measured using bioelectrical impedance analysis (BIA), and patients were classified into low and normal FFMI groups based on standard cut-off values. Clinical characteristics, GOLD airflow limitation stages based on FEV₁% predicted, GOLD ABE assessment, modified Medical Research Council (mMRC) dyspnea scale, 6-minute walk test, and BODE index were assessed and compared between groups. Results Low FFMI was present in 55.6% of patients (mean FFMI 16.17 kg/m²). Compared with normal FFMI, low FFMI was associated with higher mMRC dyspnea scores, more severe airflow limitation, lower exercise capacity, more frequent exacerbations and hospitalizations during the previous year (all p < 0.05). FFMI showed significant negative correlations with BODE index, GOLD ABE classification, and GOLD airflow limitation stage. Receiver operating characteristic (ROC) analysis demonstrated good discriminatory performance for identifying GOLD E in both males (AUC = 0.844; cut-off 15.48 kg/m²) and females (AUC = 0.785; cut-off 14.83 kg/m²). After adjustment for age, BMI, and smoking exposure in a multivariable logistic regression model, FFMI was not independently associated with GOLD E classification. In separate sensitivity models adjusted for age and smoking exposure, both FFMI (adjusted OR = 0.735, 95% CI: 0.600–0.901, p = 0.003) and BMI (adjusted OR = 0.774, 95% CI: 0.666–0.898, p = 0.001) were independently associated with GOLD group E classification. Conclusions Reduced FFMI was associated with markers of greater disease severity in COPD. Its assessment may provide complementary information regarding nutritional status and functional impairment. Prospective longitudinal studies are warranted to establish its prognostic value.