Abstract Rationale Loss of muscle mass and increased adiposity, both of which body mass index (BMI) has limited accuracy in detecting, are associated with worse outcomes across diverse populations. Moreover, the study of body composition in interstitial lung disease (ILD) is nascent. We hypothesized that lower muscle mass and higher adiposity, but not BMI, would be associated with reduced functional capacity in adults with advanced ILD, and that BMI would poorly identify abnormalities in body composition. Methods In a cross-sectional analysis of two multicenter cohort studies of lung transplant candidates with ILD, body fat percentage and muscle mass were measured by bioelectrical impedance (BIA). Sarcopenia was defined by lowest quartile of appendicular skeletal muscle index (ASMI, kg/m2). Obesity was defined as body fat percentage 40% in women and 30% in men. Functional capacity was assessed by six-minute walk distance (6MWD), gait speed over 4.57-meters, and forced vital capacity (FVC). We analyzed the association between BIA measures of body composition and BMI with 6MWD, gait speed, and FVC using multivariable linear regression adjusted for age, race, and sex. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value were calculated for BMI thresholds for identifying sarcopenia, obesity, and sarcopenic obesity (concomitant sarcopenia and obesity by BIA). Results Among 500 participants, 40% were women and 47% had idiopathic pulmonary fibrosis. By BIA, the prevalence of obesity was 40%, sarcopenia 27%, and sarcopenic obesity 12%. Each 5% increase in percent body fat by BIA was associated with decreased 6MWD (-8.6 meters, 95%CI: -15.1 to -2.2) and slower gait speed (-0.1 km/h, 95%CI: -0.2 to -0.03). Each 1 unit decrease in ASMI was associated with slower gait speed (-0.1 km/h, 95%CI: -0.3 to -0.03) and lower FVC (-116.8 ml, 95%CI: -161.4 to -72.3). Each 1 unit increase in BMI was associated with increased FVC (16.8 ml, 95%CI: 3.2 to 30.3), but BMI was not associated with 6MWD or gait speed. All BMI thresholds exhibited relatively poor PPV for identifying obesity, sarcopenia, and sarcopenic obesity (Table). Conclusions We found that lower muscle mass and higher adiposity by BIA, but not BMI, were independently associated with worse functional capacity in adults with advanced ILD. Across the BMI spectrum, BMI poorly identified obesity and sarcopenic obesity. Our findings suggest that abnormalities in muscle and fat not detected by BMI can influence key metrics in ILD. Neglecting to account for body composition may introduce unmeasured confounding to study outcomes. This abstract is funded by: NIH
Curnow et al. (Fri,) studied this question.