From the Guidelines
Acute Kidney Injury (AKI) is classified into three stages based on the KDIGO clinical practice guideline, which includes Stage 1, Stage 2, and Stage 3, defined by specific serum creatinine and urine output criteria. The staging of AKI is crucial in determining the severity of the injury and guiding treatment decisions. According to the KDIGO guideline, Stage 1 AKI is defined as an increase in serum creatinine by 0.3 mg/dL within 48 hours or an increase to 1.5-1.9 times baseline, or urine output less than 0.5 mL/kg/h for 6-12 hours 1. Stage 2 AKI is defined as an increase in serum creatinine to 2.0-2.9 times baseline or urine output less than 0.5 mL/kg/h for 12 hours. Stage 3 AKI is defined as an increase in serum creatinine to 3.0 times baseline or an increase to 4.0 mg/dL, or initiation of renal replacement therapy, or a decrease in estimated glomerular filtration rate (eGFR) to less than 35 mL/min/1.73 m2, or urine output less than 0.3 mL/kg/h for 24 hours or anuria for 12 hours.
The KDIGO guideline is the most recent and widely accepted classification system for AKI, and it has been endorsed by several international organizations, including the Kidney Disease Improving Global Outcomes (KDIGO) and the National Institute for Health and Care Excellence (NICE) 1. The guideline emphasizes the importance of early detection and staging of AKI, as well as the need for ongoing monitoring and management to prevent progression to more severe stages.
Some key points to note about the KDIGO guideline include:
- The use of serum creatinine and urine output criteria to define AKI stages
- The importance of considering baseline renal function and comorbidities when interpreting AKI stages
- The need for ongoing monitoring and management to prevent progression to more severe stages
- The use of renal replacement therapy as a criterion for Stage 3 AKI
Overall, the KDIGO guideline provides a standardized framework for defining and staging AKI, which can help clinicians to identify patients at risk of AKI and to provide timely and effective treatment to improve outcomes.
From the Research
Definition and Staging of Acute Kidney Injury (AKI)
The Kidney Disease: Improving Global Outcomes (KDIGO) defines AKI as an increase in the serum creatinine (SCr) level of 0.3 mg/dL or more within 48 hours, an SCr level increase of 1.5 times or more of the baseline level within 7 days, or a decrease in urine output to less than 0.5 mL/kg/hour for 6 hours 2, 3, 4.
Grades of Acute Kidney Injury (AKI)
The grades of AKI are typically classified into three stages:
- Stage 1: defined as an increase in SCr of 0.3 mg/dL or more within 48 hours or a 1.5-1.9 times increase in SCr from baseline within 7 days, or a decrease in urine output to less than 0.5 mL/kg/hour for 6-12 hours 2, 4, 5.
- Stage 2: defined as a 2.0-2.9 times increase in SCr from baseline within 7 days, or a decrease in urine output to less than 0.5 mL/kg/hour for more than 12 hours 2, 4, 6.
- Stage 3: defined as a 3.0 times or more increase in SCr from baseline within 7 days, or a decrease in urine output to less than 0.3 mL/kg/hour for more than 24 hours, or the initiation of renal replacement therapy 2, 4, 6.
Additional Sub-Classification
Some studies suggest further categorizing AKI stage 1 into two sub-stages:
- Stage 1a: an absolute increase in serum creatinine of 0.3 mg/dL within 48 hours
- Stage 1b: a 50% relative increase in serum creatinine within 7 days 5.
Key points to note about AKI staging include:
- The KDIGO criteria do not rely on changes in GFR for staging except in children under the age of 18 years 4.
- AKI misclassification may result from the lack of a uniform approach to estimate baseline SCr and the changes in SCr concentrations resulting from acute severe illness and altered fluid balance 4.
- The existing definitions of AKI rely on imperfect markers of renal function rather than direct measures of kidney damage, but remain an important diagnostic and prognostic tool 4.