Creatinine Paradox in CRRT: Higher Levels, Lower Mortality – A MIMIC-IV Validation Study

The relationship between baseline serum creatinine (SCr) levels at the initiation of continuous renal replacement therapy (CRRT) and in-hospital mortality remains unclear. This study aimed to investigate this relationship in critically ill patients with acute kidney injury (AKI) undergoing CRRT. Methods: In this retrospective cohort study, data from the Medical Information Mart for Intensive Care IV (MIMIC-IV 2.2) database were categorized into four quartiles based on SCr levels at CRRT initiation, with in-hospital mortality as the primary outcome. We applied Kaplan-Meier curves for outcome comparison across groups. Multivariate Cox proportional-hazards models and restricted cubic splines (RCS) were conducted to examine the association between initial SCr and mortality. Additional interaction and subgroup analyses were conducted to reinforce our findings. Results: In a cohort of 989 AKI patients undergoing CRRT, the mean age was 62.5 years, with 60% being male and an in-hospital mortality rate of 47.5%. Kaplan-Meier curve analysis revealed that higher SCr levels were linked to a lower risk of in-hospital mortality. Cox proportional hazards regression confirmed a significant increase in mortality risk among patients in the lowest SCr quartile. Furthermore, RCS analysis demonstrated an L-shaped relationship between SCr and in-hospital mortality, with an inflection point at 5.75 mg/dL. No interactions were found between SCr and in-hospital mortality. Conclusions: In critically ill AKI patients requiring CRRT, a paradoxical L-shaped relationship between SCr levels and in-hospital mortality risk was observed, with an inflection point at 5.75 mg/dL. Further large, diverse studies are needed to confirm these results.