From the Guidelines
Mild Acute Kidney Injury (AKI) is expected to have a urine output of less than 0.5 mL/kg/h for more than 6 hours.
Definition and Staging of AKI
According to the KDIGO guidelines 1, AKI is defined as an increase in serum creatinine (SCr) by 0.3 mg/dL within 48 hours, or an increase in SCr to 1.5 times baseline, which is known or presumed to have occurred within the prior 7 days, or a urine volume of 0.5 mL/kg/h for 6 hours.
- The staging of AKI is based on the severity of the injury, with stage 1 being the least severe and stage 3 being the most severe.
- The criteria for each stage are as follows: + Stage 1: Increase in SCr to 1.5-1.9 times baseline, or urine output of less than 0.5 mL/kg/h for more than 6 hours. + Stage 2: Increase in SCr to 2.0-2.9 times baseline, or urine output of less than 0.5 mL/kg/h for more than 12 hours. + Stage 3: Increase in SCr to 3.0 times baseline, or increase in SCr to 4.0 mg/dL, or initiation of renal replacement therapy, or urine output of less than 0.3 mL/kg/h for 24 hours or anuria for 12 hours.
Urine Output in Mild AKI
In patients with mild AKI, the urine output is expected to be less than 0.5 mL/kg/h for more than 6 hours, but more than 0.5 mL/kg/h for 6-12 hours 1, 2.
- This decrease in urine output is a key indicator of AKI and should be monitored closely in patients at risk of developing AKI.
- The use of urine output as a criterion for AKI diagnosis is supported by several studies, including those by Chertow et al. 2, which showed that small rises in creatinine are independently associated with increased mortality.
Limitations and Controversies
There are some limitations and controversies surrounding the use of urine output as a criterion for AKI diagnosis, including the lack of standardization in measuring urine output and the potential for variability in reporting AKI incidence 3.
- However, the KDIGO guidelines recommend that both urine output and serum creatinine level should continue to be used in the diagnosis and staging of AKI, and that further research is needed to clarify the role of these measurements in AKI diagnosis and management.
From the Research
Definition of Acute Kidney Injury (AKI)
The definition of AKI is based on the increase in serum creatinine levels or decrease in urine output, as established by the Kidney Disease: Improving Global Outcomes (KDIGO) group 4, 5.
Urine Output Criterion for AKI
The urine output criterion for AKI is defined as a urine volume less than 0.5 ml/kg/hour for at least 6 hours 4, 6, 5.
Expected Urine Output in Mild AKI
In patients with mild AKI, the expected urine output is less than 0.5 ml/kg/hour for at least 6 hours, according to the KDIGO definition 4, 5.
- The urine output criterion is used to diagnose and stage AKI, with a decrease in urine output indicating a higher stage of AKI 6, 7.
- The measurement of urine output can be done using consecutive hourly readings or mean output, which can affect the reported incidence and staging of AKI 7.
- The definition of hourly urine output influences the reported incidence and staging of AKI, with the use of mean hourly urine output leading to a higher reported incidence of AKI 7.