Elevated atherogenic index of plasma is associated with severe acute kidney injury in critically ill patients with cardiovascular disease – a MIMIC-IV analysis with external validation in the eICU-CRD database

The atherogenic index of plasma (AIP) is a lipid-based marker of cardiovascular risk, yet its prognostic value for severe acute kidney injury (AKI) in critically ill patients with cardiovascular disease (CVD) remains uncertain. This retrospective study analyzed 5,872 patients from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database, with external validation in the eICU Collaborative Research Database (eICU-CRD). The primary outcome was stage 3 AKI, and secondary outcomes included renal replacement therapy (RRT) and length of stay. Stage 3 AKI was observed in 20.7% of patients, with the incidence increasing across AIP quartiles (Q1–Q4: 15.9–26.8%), and 5.3% of patients requiring RRT (Q1–Q4: 2.6–10.9%). High AIP was associated with stage 3 AKI (adjusted OR = 1.35; 95% CI: 1.11–1.64), RRT (OR = 1.95; 95% CI: 1.33–2.87), longer hospital LOS (β = 3.58; p < 0.001) and ICU LOS (β = 1.14; p < 0.001). Restricted cubic splines revealed linear associations between AIP and both renal outcomes (stage 3 AKI and RRT). Mediation analysis indicated that stage 3 AKI mediated 12.6% of the association between the AIP and in-hospital mortality. The predictive models achieved AUCs of 0.916 for RRT and 0.727 for stage 3 AKI. These associations with renal outcomes were robust, as confirmed by entropy balancing and external validation in the eICU-CRD. Elevated AIP is a robust, externally validated predictor of stage 3 AKI and RRT, with substantial predictive accuracy for RRT. Furthermore, it appears to influence in-hospital mortality partially through renal injury, warranting confirmation in future prospective studies.