Classifying AKI by Urine Output versus Serum Creatinine Level

Severity of AKI is determined by the magnitude of increase in serum creatinine level or decrease in urine output. However, patients manifesting both oliguria and azotemia and those in which these impairments are persistent are more likely to have worse disease. Thus, we investigated the relationship of AKI severity and duration across creatinine and urine output domains with the risk for RRT and likelihood of renal recovery and survival using a large, academic medical center database of critically ill patients. We analyzed electronic records from 32,045 patients treated between 2000 and 2008, of which 23,866 (74.5%) developed AKI. We classified patients by levels of serum creatinine and/or urine output according to Kidney Disease Improving Global Outcomes staging criteria for AKI. In-hospital mortality and RRT rates increased from 4.3% and 0%, respectively, for no AKI to 51.1% and 55.3%, respectively, when serum creatinine level and urine output both indicated stage 3 AKI. Both short- and long-term outcomes were worse when patients had any stage of AKI defined by both criteria. Duration of AKI was also a significant predictor of long-term outcomes irrespective of severity. We conclude that short- and long-term risk of death or RRT is greatest when patients meet both the serum creatinine level and urine output criteria for AKI and when these abnormalities persist.