Supplementary Material for: Reduction Rate of Uric Acid in Blood During Continuous Renal Replacement Therapy for Acute Kidney Injury: A Multicenter Retrospective Observational Study

Introduction: Continuous renal replacement therapy (CRRT) eliminates these small solutes with equal efficacy under the same conditions. However, variations in the reduction rates of these solutes observed in patients with CRRT are likely influenced by factors other than removal through CRRT. This study evaluated the reduction rates of these small solutes during CRRT and their possible association with mortality.
Methods: This study used the data of limited patients registered in the CHANGE study, which is a large retrospective observational study on CRRT management across 18 Japanese ICUs. Reduction rates of three solutes in blood, calculated on the 1st and 2nd days, were compared in patients with acute kidney injury (AKI) treated by CRRT. The potential association between solute reduction rates and mortality during CRRT or within 7 days after the termination of CRRT was evaluated.
Results: In total, 163 patients with AKI were included in the analysis. The reductuin rates of uric acid (UA) were significantly higher than those of urea and creatinine for the 1st and 2nd tests in the entire cohort. Receiver operating curve (ROC) analysis revealed that lower UA reduction rates were significantly associated with mortality during CRRT or within 7 days after CRRT termination (area under the ROC curve: 0.62 [95% confidence interval {CI} 0.52–0.71] for the 1st test and 0.63 [95%CI 0.54–0.72] for the 2nd test). After adjusting for age and SOFA score, a significant association was observed between lower UA reduction rates and hospital mortality for both tests.
Conclusion: Among the small solutes, UA reduction rates in patients with AKI treated with CRRT were notably higher than those of creatinine and urea. Furthermore, the significant association between lower UA reduction rates and mortality suggests that UA reduction rate may serve as a valuable indicator of insufficient removal of uremic solutes by CRRT, although the decline in UA production must be taken into account.