Association of Oliguria With Acute Kidney Injury, Chronic Kidney Disease, and Mortality: Determining the Optimal Threshold in Critically Ill Patients

Objectives: Oliguria is a key prognostic indicator of acute kidney injury (AKI), yet the consensus definition (< 0.5 mL/kg/hr) is increasingly questioned. We aimed to determine thresholds of lowest mean diuresis (LMD) associated with AKI, chronic kidney disease (CKD), and mortality. Design: Retrospective observational study. Setting: Uppsala University Hospital ICU, Sweden. Patients: A total of 4999 adults (≥ 18 yr) without preexisting CKD admitted to the ICU between 2017 and 2024. Interventions: None. Measurements and Main Results: LMD was calculated over 3, 6, 12, and 24 hours (LMD3h–LMD24h). Generalized additive models were used, adjusting for Simplified Acute Physiology Score 3 estimated mortality ratio and gender. Outcomes were AKI within 7 days of LMD (Kidney Disease Improving Global Outcomes creatinine criteria), incident CKD after ICU discharge, and 90-day mortality. All LMD time frames were significantly associated with AKI, CKD, and death ( p < 0.0001). Thresholds for AKI were 0.43, 0.41, 0.42, and 0.53 mL/kg/hr; for CKD, 0.21, 0.21, 0.31, and 0.43 mL/kg/hr; and for mortality 0.16, 0.18, 0.24, and 0.39 across LMD3h–LMD24h. Conclusions: The risk of mortality or persistent kidney injury, reflected by incident CKD, increases at a lower urine output threshold than the current AKI definition. These findings support the idea of filtration deficit, urine output, and tissue injury as different dimensions of AKI and should influence future AKI definitions.