The association of early glomerular filtration kinetics and urinary urea excretion with subsequent renal replacement therapy under a delayed strategy in severe acute kidney injury

In severe acute kidney injury (AKI), delayed renal replacement therapy (RRT) strategies allow many KDIGO stage-3 patients to avoid dialysis, but excessive postponement in those who ultimately require RRT may worsen outcomes. Early physiologically grounded markers to identify patients likely to need RRT are lacking. We evaluated whether combining early glomerular filtration kinetics and timed urinary urea excretion could improve discrimination of subsequent RRT initiation under a delayed strategy. TUBSAKI is a prospective bicentric ICU cohort including adults with KDIGO stage-3 AKI managed with a protocolized delayed RRT strategy. Blood and 24-hour urine samples were collected at diagnosis (D0) and day 1 (D1). Glomerular filtration dynamics were assessed using kinetic GFR (kGFR), and timed urinary urea excretion was assessed using UUEI. Discrimination for subsequent RRT was assessed using ROC curves and AUC. A combined logistic model (kGFR D0-D1 + UUEI D1) was internally validated by bootstrap, with sensitivity analyses adjusted for SOFA and KDIGO stage-3 oliguria. Among 110 patients, 31 (28%) required RRT. kGFR D0-D1 showed good discrimination (AUC 0.81 0.72–0.89), and UUEI D1 moderate discrimination (AUC 0.74 0.63–0.82). The combined model showed an AUC of 0.85 (0.76–0.91), optimism-corrected AUC 0.83, and acceptable calibration. Discrimination remained stable after adjustment for SOFA and oliguria. Incremental gain over kGFR alone was modest and not statistically significant. Early glomerular filtration kinetics and urinary urea excretion were associated with subsequent RRT initiation under a delayed strategy. The incremental clinical value of UUEI remained limited in this cohort, and external validation is required before clinical use.