Long-term mortality after stage 1 acute kidney injury in critically ill patients - an observational cohort study

Background: Acute Kidney Injury (AKI) is prevalent in intensive care units (ICU) and is linked with increased mortality. The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines define AKI using serum creatinine and urinary output criteria. While moderate and severe AKI according the creatinine criterion correlate with increased mortality, the significance of stage 1 AKI remains debated. Methods: Retrospective cohort analysis from two tertiary care centres in Switzerland and Austria (2013-2021) to investigate the association between stage 1 AKI (KDIGO creatinine criterion) in the first seven days after ICU admission and one-year mortality in adult ICU patients. Data were extracted using standardized protocols. Baseline creatinine was determined using estimation formulas. We applied multivariable regression models adjusted for key confounders and conducted sensitivity analyses. Results: Of 42,446 patients, 4667 (11 %) developed stage 1 AKI, 13 % (n = 5449) moderate/ severe AKI and 32,330 patients no AKI (76 %). Stage 1 AKI associates with one-year mortality (OR 1.6 [95 %CI 1.48; 1.73], p < 0.001) and increases length of stay in ICU (beta 1.4 [95 %CI 1.2; 1.5], p < 0.001) and hospital (beta 2.7 [95 %CI 2.1; 3.2], p < 0.001). In subgroup-analyses, we observed similar associations in patients with surgery (OR 1.66 [95 %CI 1.45;1.89], p < 0.001) and without surgery (OR 1.61 [95 %CI 1.46;1.78], p < 0.001). Conclusion: Stage 1 AKI is associated with 1-year mortality in adult ICU patients even in steps below 26.5 mu mol/L. This highlights the prognostic significance of subclinical renal injury and underlines the need for increased efforts to diagnose AKI in its full spectrum. The analysis is limited by basing the AKI diagnosis on creatinine criterion.