Oliguria is an early predictor of higher mortality in critically ill patients

Oliguria is a valuable marker of kidney function and a criterion for diagnosing and staging acute kidney injury (AKI). However, the utility of urine output as a specific metric for renal dysfunction is somewhat controversial. To study this issue further we tested whether urine output is a sensitive, specific, and early measure for diagnosing and staging AKI in 317 critically ill patients in a prospective observational study. Urine output was assessed every hour and serum creatinine every 12 to 24h. The sensitivity and specificity of different definitions of oliguria for the diagnosis of AKI were compared with the Acute Kidney Injury Network serum creatinine criterion. The incidence of AKI increased from 24%, based solely on serum creatinine, to 52% by adding the urine output as a diagnostic criterion. Oliguric patients without a change in serum creatinine had an intensive care unit mortality rate (8.8%) significantly higher than patients without AKI (1.3%), and similar to oliguric patients with an increase in serum creatinine (10.4%). The diagnosis of AKI occurred earlier in oliguric than in non-oliguric patients. Oliguria of more than 12h and oliguria of 3 or more episodes were associated with an increased mortality rate. Thus, urine output is a sensitive and early marker for AKI and is associated with adverse outcomes in intensive care unit patients.