Creatinine-Cystatin C Ratio and Mortality in Patients Receiving Intensive Care and Continuous Kidney Replacement Therapy: A Retrospective Cohort Study

Rationale & Objective: Studies have suggested associations between lower ratios of serum creatinine to cystatin C with both lower muscle mass and adverse clinical outcomes in multiple disease conditions. Identifying risk factors for mortality among patients with acute kidney injury (AKI) undergoing continuous kidney replacement therapy (CKRT) may improve assessment of prognosis. We sought to evaluate the association of creatinine-cystatin C ratio with outcomes in patients with AKI undergoing CKRT. Study Design: Retrospective cohort study. Setting & Participants: 1,588 patients treated with intensive care and CKRT for AKI at a tertiary Korean medical center. Predictor: Baseline serum creatinine-cystatin C ratio at the time of CKRT initiation. Outcomes: Age- and sex-adjusted 90-day mortality after CKRT initiation. Analytical Approach: Cox proportional hazard models to estimate the association between creatinine-cystatin C ratio and outcome. Results: Mean age was 64.7 +/- 14.5 years and 635 patients (40.0%) were women. The range of creatinine-cystatin C ratios was 0.08 to 10.48. The 30- and 90-day mortality rates were significantly lower for the higher creatinine-cystatin C ratio groups. Multivariable Cox proportional hazards regression analyses revealed that mortality risk became successively lower across quartiles of greater creatinine-cystatin C ratio. When creatinine-cystatin C ratio was evaluated using cubic spline analyses, risks for both 30- and 90-day mortality were lower with higher creatinine-cystatin C ratios. These associations remained significant even after adjustment for confounding variables. Limitations: Retrospective analysis, serum creatinine and cystatin C may not be in steady state in the setting of AKI. Conclusions: Higher serum creatinine-cystatin C ratios were associated with better survival in patients receiving intensive care and CKRT.