The Change in Muscle Mass Among Kidney Transplant Recipients: A Prospective Cohort Study

•We carried out a prospective cohort study with 1-year follow-up.•We investigated muscle mass change and its risk factors in kidney transplant recipients.•Muscle mass increased in most of the kidney transplant recipients.•Age and BMI might be the risk factors for the change in muscle mass. Recovery of renal function after transplantation leads to improved uremic conditions, increased physical activity, and liberation from severe dietary restrictions. Consequently, the muscle mass of kidney transplant recipients increases for several years after their transplant. However, the change in muscle mass and its associated factors among these patients remain largely unknown. Herein, we carried out a prospective cohort study with 1-year follow-up to investigate how muscle mass changes and to identify its risk factors among kidney transplant recipients. We performed a single-center, 1-year, prospective, observational cohort study from August 2017 to February 2019 at Osaka City University Hospital in Japan. The skeletal muscle mass index (SMI) was measured by bioelectrical impedance analysis. The risk factors related to the change in muscle mass were analyzed using multivariate linear regression models of age, sex, body mass index (BMI), dialysis vintage, transplant vintage, diabetes mellitus, hemoglobin, C-reactive protein, estimated glomerular filtration rate, and SMI at baseline. A total of 180 kidney transplant recipients were enrolled in the present study. The median age was 55 years, and the median transplant vintage was 78 months. The median rate of change in SMI was +2.07%, and SMI increased in 118 (66%) patients during the 1-year follow-up. By multivariate analysis, the change in SMI at 1-year follow-up was independently associated with age (P = 0.017) and BMI (P = .023). SMI increased in most of the kidney transplant recipients, and age and BMI might be the risk factors for this change in muscle mass among these patients.