Cystatin C vs creatinine eGFR in advanced CKD: an analysis of the STOP-ACEi trial.

Background: In this secondary analysis of the STOP-ACEi trial, we explored the impact of discontinuing or continuing renin-angiotensin system inhibitor therapy in people with advanced chronic kidney disease on cystatin C estimated glomerular filtration rate (eGFR). Methods: Cystatin C eGFRs were calculated at baseline, 12, 24 and 36 months using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) cystatin 2012, European Kidney Function Consortium and CKD-EPI Combined 2021 equations. We excluded samples obtained after the initiation of kidney replacement therapy. Primary analysis used complete case analysis and mixed-effects linear regression model, adjusting for minimization variables, baseline value, time-point and treatment by time interaction. Sensitivity analysis was conducted using a pattern mixture model to account for missing data that was not at random. To model the longitudinal cystatin C data with time-to-event data, a joint model was utilized which incorporated the cystatin C measurements at various time points and accounted for the occurrence of kidney replacement therapy. Results: The mean cystatin C eGFRs (CKD-EPI 2012) at baseline were 17.8 mg/L [standard deviation (SD 6.3)] and 17.9 mL/min/1.73 m Conclusion: Our results are consistent with the primary study's analysis and sensitivity analyses support these findings and provide additional insights. Our findings demonstrate the similarity of creatinine and cystatin eGFR results and therefore support the use of cystatin C as an alternative marker of eGFR in advanced CKD, particularly in those in whom creatinine is likely to be less accurate.