From the Guidelines
Acute kidney injury (AKI) is calculated using changes in serum creatinine levels and/or urine output over time, with the most recent and highest quality study 1 defining AKI as an increase in creatinine by 0.3 mg/dL within 48 hours or an increase in serum creatinine to 1.5 times baseline within 7 days or urine volume 0.5 mL/kg/hr for 6 hours.
Definition and Staging of AKI
The definition and staging of AKI are crucial for early identification and management of kidney injury.
- The KDIGO guidelines, as referenced in 1, provide a widely accepted framework for defining and staging AKI.
- According to these guidelines, AKI is defined as any of the following:
- An increase in serum creatinine by ≥0.3 mg/dL within 48 hours
- An increase in serum creatinine to ≥1.5 times baseline within 7 days
- Urine volume <0.5 mL/kg/hour for 6 hours
Importance of Early Detection
Early detection of AKI is critical for improving patient outcomes, as it allows for prompt intervention and management of underlying causes.
- The use of serum creatinine and urine output criteria, as outlined in 1, enables clinicians to identify kidney injury early, even before symptoms develop.
- The staging of AKI, from 1 to 3, based on the magnitude of creatinine increase or decrease in urine output, helps guide treatment decisions and prognostication.
Clinical Application
In clinical practice, the calculation of AKI should be based on the most recent and reliable serum creatinine and urine output data available.
- Clinicians should be aware of the potential limitations and uncertainties in the definition and staging of AKI, as discussed in 1, 1, and 1.
- However, the KDIGO guidelines, as referenced in 1, provide a widely accepted and evidence-based framework for defining and staging AKI, and should be used as the primary guide for clinical decision-making.
From the Research
Definition and Calculation of Acute Kidney Injury
The calculation of acute kidney injury (AKI) is based on the increase in serum creatinine levels and/or decrease in urine output. According to the Kidney Disease: Improving Global Outcomes (KDIGO) group 2, AKI is defined as:
- An increase in serum creatinine levels by at least 0.3 mg/dl within 48 hours
- A 1.5-fold increase in serum creatinine levels from the baseline, which is known or presumed to have occurred within the preceding 7 days
- A urine output of less than 0.5 ml/kg/hour for at least 6 hours
Classification Systems for AKI
Several classification systems have been developed to define and stratify the severity of AKI, including:
- RIFLE (Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease) classification, which relies on changes in serum creatinine or glomerular filtration rates and/or urine output 3
- AKIN (Acute Kidney Injury Network) classification, a modified version of the RIFLE classification 4, 3
- KDIGO classification, which unified the definition of AKI in 2012 2
Importance of Urine Output Criteria
The use of urine output criteria in addition to serum creatinine levels is important for the accurate diagnosis of AKI. A study found that discarding the urine output criteria significantly underestimated the presence and grade of AKI, delayed the diagnosis of AKI, and was associated with higher mortality 5.
Limitations of Current Diagnostic Methods
Current diagnostic methods for AKI, including serum creatinine and urine output, have limitations, and novel biomarkers have been developed to detect cellular stress or damage 4, 6. Persistent AKI and acute kidney disease are relatively new concepts that explore the idea of AKI as a continuum with chronic kidney disease 6.