Renal Angina Index for Predicting Acute Kidney Injury in Adult ICU Patients

Acute kidney injury (AKI) is a frequent complication of critical illness and is associated with increased morbidity and mortality. Early identification of patients at risk of progressing to moderate-to-severe AKI may facilitate closer monitoring and timely implementation of kidney-protective strategies. This prospective observational cohort study will evaluate the predictive performance of the Renal Angina Index (RAI) for the development of Kidney Disease: Improving Global Outcomes (KDIGO) stage 2 or stage 3 AKI in adult intensive care unit patients. Consecutive eligible patients admitted to the participating adult intensive care unit will be enrolled. The RAI will be calculated 24 hours after ICU admission using routinely available clinical characteristics and the change in serum creatinine between ICU admission and 24 hours. The primary outcome will be the development of KDIGO stage 2 or stage 3 AKI during the subsequent 48 hours. AKI staging will incorporate serum creatinine, urine-output, and renal replacement therapy criteria according to KDIGO definitions. The predictive performance of RAI will be evaluated using receiver operating characteristic analysis and the prespecified RAI threshold of ≥10. Secondary outcomes will include 7-day and 30-day intensive care unit mortality, intensive care unit length of stay, and duration of invasive mechanical ventilation.

Inclusion Criteria: * Age 18 years or older. * Admission to the participating adult intensive care unit. * Availability of serum creatinine measurements at ICU admission and 24 hours after ICU admission. * Availability of a stable outpatient serum creatinine measurement obtained within the 6 months preceding ICU admission that can be used as the baseline value for KDIGO acute kidney injury staging. * Availability of the clinical and laboratory data required to calculate the Renal Angina Index at 24 hours after ICU admission. * Availability of serum creatinine and urine-output data required for assessment of the primary outcome during the 48 hours following Renal Angina Index calculation. * Written informed consent from the participant or a legally authorized representative. Exclusion Criteria: * Age younger than 18 years. * KDIGO stage 2 or stage 3 acute kidney injury present at ICU admission or developing before calculation of the Renal Angina Index at 24 hours after ICU admission. * Initiation of acute renal replacement therapy before calculation of the Renal Angina Index. * End-stage kidney disease requiring chronic renal replacement therapy. * History of kidney transplantation. * Absence of an eligible stable outpatient baseline serum creatinine measurement within the 6 months preceding ICU admission. * Death, discharge, or transfer from the ICU within the first 24 hours after admission, preventing calculation of the Renal Angina Index. * Insufficient data for assessment of the primary outcome during the 48-hour period following Renal Angina Index calculation. * Pregnancy.