Discordance between creatinine and cystatin C-based estimation of glomerular filtration rate (eGFR) in solid organ transplant patients.

Abstract

Background: Estimation of glomerular filtration rate is a critical component of assessing kidney function post-solid organ transplantation and in monitoring risk of acute injury. Our objective was to evaluate estimated glomerular filtration rate (eGFR) as derived from creatinine (eGFR_cr), cystatin C (eGFR_cys), and both (eGFR_cr-cys) in a cohort of transplant recipients.

Methods: A total of 47 unique post-solid organ transplant patients receiving tacrolimus were included. Residual specimens were assayed for creatinine (Jaffe and enzymatic), cystatin C, and tacrolimus. eGFR was estimated using the 2021 chronic kidney disease (CKD)-EPI formulae. Results were compared by Deming regression and bias was assessed using non-parametric cumulative distribution plots. Percent agreement in chronic kidney disease (CKD) by stage was evaluated across equations.

Results: eGFR_cr relative to eGFR_cys estimates demonstrated a median bias of -22 mL/min/1.73 m² and an overall 21.3 % [95 % CI: 12.1, 35.0] agreement in CKD staging. eGFR_cr-cys demonstrated a median bias of -14 mL/min/1.73 m² and overall agreement of 34.0 % [95 % CI: 22.3, 48.4] relative to eGFR_cr (enzymatic). Discordance increased proportionally with eGFR and did not differ by creatinine assay (Jaffe or enzymatic).

Conclusion: Cystatin C incorporation leads to markedly negative biases between eGFR estimates in patients with solid organ transplant, implying lack of applicability in the transplant setting. This highlights the dependency of patient characteristics on equation performance and the need to consider confounding factors in interpretation and utilization of cystatin C based equations.