Low Cystatin C-to-Creatinine Estimated GFR Ratio Predicts Post-Kidney Transplant Cardiovascular Events

A low cystatin C-based to creatinine-based estimated glomerular filtration rate (eGFR) ratio (eGFR_cys/eGFR_cr) is associated with poor clinical outcomes, but data in kidney transplant recipients (KTRs) remain limited. We aimed to investigate the association between low eGFR_cys/eGFR_cr and allograft loss, major adverse cardiovascular events (MACEs) and mortality, and to identify the reasons for such a low ratio.

This single-center retrospective study included KTRs with eGFR_cys/eGFR_cr determined 3 months posttransplant using the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) and the European Kidney Function Consortium (EKFC) equations. Body composition data were obtained from a computed tomography (CT) slice at the third lumbar vertebra as follows: skeletal muscle mass index (SMI: cross-sectional muscle area divided by height squared), myosteatosis (mean muscle CT attenuation), as well as subcutaneous and visceral adipose tissue indexes.

Among 385 KTRs, an eGFR_cys/eGFR_cr < 0.7 was found in 106 (27.5%) and 54 (14%) patients with the CKD-EPI and EKFC equations, respectively. A low eGFR_cys/eGFR_cr ratio was independently associated with MACEs whatever the equation considered (adjusted hazard ratio [aHR]: 2.46; 95% confidence interval [CI]: 1.24-4.87 for CKD-EPI, and aHR: 2.29; 95% CI: 1.11-4.72 for EKFC), but not with death or allograft loss. Using CKD-EPI equations, diabetes mellitus was associated with eGFR_cys/eGFR_cr < 0.7; using EKFC equations, diabetes mellitus and male sex were associated. In the 275 KTRs with available CT scan, male sex and myosteatosis were associated with low eGFR_cys/eGFR_cr ratio, together with low SMI for CKD-EPI equations, and diabetes mellitus for EKFC.

A low eGFRcys/eGFRcr in KTRs is associated with MACEs. Diabetes mellitus, male sex, myosteatosis, and low muscle mass could be key factors of such a low ratio.