The sarcopenia index: A novel measure of muscle mass in lung transplant candidates

Background: Frailty, including low muscle mass, is an emerging risk factor for poor outcomes after lung transplant. The sarcopenia index (SI)—(serum creatinine value/cystatin C value) × 100—is a novel blood test to approximate muscle mass. We sought to validate SI among lung transplant patients. Methods: We retrospectively identified adult lung transplant recipients from 2000 through 2012 at our institution who underwent computed tomography within 1 year before transplant and had preserved blood samples. Creatinine and cystatin C values were measured using the samples and used to calculate SI. Muscle mass was estimated by computed tomographic measurement of skeletal muscle cross-sectional surface area (SA) at the L1 to L3 vertebral levels. Correlation between SI and SA was evaluated. Results: Of 28 patients meeting eligibility criteria, most were white (96%) and men (54%). Median (interquartile range) body mass index, SI, and SA were 25.9 (22-30) kg/m ² , 106 (91-119), and 157 (113-195) cm2, respectively. The Pearson correlation coefficient between SI and SA was significant at L2 (0.43; P =.02) and L3 (0.41; P =.03). Conclusion: Sarcopenia index is a potentially objective measure for estimating muscle mass that is noninvasive and less expensive. Sarcopenia index could be considered in lung transplant candidate selection following prospective validation in larger cohorts.