Sequential Computed Tomography Morphometry-derived Muscle Loss Is Associated With Kidney Dysfunction and Mortality in Kidney Transplant Recipients Undergoing Serial Clinically Indicated Computed Tomography Imaging.

Background: Kidney transplantation is the optimal treatment for end-stage kidney disease, yet long-term outcomes remain heterogeneous, underscoring the need for improved clinical risk stratification. Sarcopenia assessed by computed tomography (CT)-based morphometry has emerged as a promising biomarker across multiple conditions, including solid organ transplantation. Importantly, muscle metrics can be derived from CT scans obtained for clinical indications, enabling opportunistic screening without additional imaging burden. However, longitudinal muscle trajectories after kidney transplantation derived from indication-driven CT imaging and their associations with graft dysfunction and survival remain poorly characterized. Methods: In this retrospective single-center study, CT morphometry at the L3 level was analyzed in kidney transplant recipients who underwent 2 clinically indicated abdominal CT scans. Skeletal Muscle Index, Paraspinal Muscle Index, Psoas Muscle Index, and visceral adipose tissue were quantified. Longitudinal changes between both time points were related to kidney allograft dysfunction, defined as major adverse kidney events, and overall survival. Survival analyses were performed using Kaplan-Meier estimates and Cox proportional hazards models. Results: Seventy-three kidney transplant recipients were included. Patients with allograft dysfunction demonstrated markedly accelerated muscle loss compared with those maintaining stable graft function. Muscle decline was primarily driven by progression to end-stage kidney disease, whereas isolated ≥25% estimated glomerular filtration rate decline without graft failure was not associated with significant sarcopenia progression. Adverse CT morphometry was independently associated with reduced survival in Kaplan-Meier and multivariable Cox regression analyses adjusted for age, sex, and major adverse kidney events. Conclusions: Among kidney transplant recipients undergoing indication-driven imaging, posttransplant skeletal muscle loss is closely linked to allograft dysfunction and independently associated with mortality. Opportunistic CT-based morphometry may therefore represent a valuable tool for risk stratification in vulnerable transplant populations. Prospective studies are warranted to validate these findings and assess interventional implications.