What are the criteria for Acute Kidney Injury (AKI)?

From the Guidelines

Acute Kidney Injury (AKI) criteria are based on an increase in serum creatinine or a decrease in urine output within 48 hours to 7 days.

Criteria for AKI

The criteria for AKI, as defined by the Kidney Disease Improving Global Outcomes (KDIGO) guideline, include:

• Stage 1: Rise of >26 mmol/l or 0.3 mg/dl within 48 h or 50–99% creatinine rise from baseline within 7 days, and/or urine output <0.5 ml/kg/h for more than 6 h 1
• Stage 2: 100–199% creatinine rise from baseline within 7 days, and/or urine output <0.5 ml/kg/h for more than 12 h 1
• Stage 3: >200% creatinine rise from baseline within 7 days, or current creatinine ≥354 mmol/l, with either a rise of >26 mmol/l or 0.3 mg/dl within 48 h or >50% creatinine rise from baseline within 7 days, and/or urine output <0.3 ml/kg/h for 24 h or anuria for 12 h, or any requirement for renal replacement therapy 1

Key Points

• The KDIGO guideline merged the RIFLE and AKIN criteria, and is currently the most widely accepted definition of AKI 1
• The definition of AKI includes a sudden decrease in glomerular filtration rate (GFR) manifested by an increase in serum creatinine or oliguria within 48 hours to 7 days 1
• The severity of AKI is determined by the severity of increase in serum creatinine or oliguria 1
• The urine output criteria for AKI are applicable only in intensive-care settings, and ascertainment of AKI and its severity from the timing of changes in serum creatinine level alone is generally acceptable in other settings 1

From the Research

Definition and Classification of Acute Kidney Injury (AKI)

The criteria for AKI have been defined by several studies, including the RIFLE and AKIN criteria.

• The RIFLE criteria, published by the Acute Dialysis Quality Initiative Group, define AKI as an increase in serum creatinine level or a decrease in urine output 2.
• The AKIN criteria, proposed by the Acute Kidney Injury Network, modify the RIFLE criteria to include an absolute serum creatinine change of 0.3 mg/dl in a 48-hour period to establish the diagnosis of AKI 3.

Comparison of RIFLE and AKIN Criteria

Studies have compared the performance of the RIFLE and AKIN criteria for diagnosis and classification of AKI.

• One study found that the AKIN criteria slightly increased the number of patients classified as Stage I injury, but decreased the number of patients classified as having Stage II injury compared to the RIFLE criteria 2.
• Another study found that the AKIN criteria were more precise and predictive of death than the RIFLE criteria in burn patients 3.

Limitations of Current Criteria

The current criteria for AKI have several limitations, including the use of surrogate markers of renal impairment that manifest relatively late after injury has occurred 4.

• New biomarkers for AKI have shown promise for early diagnosis and prediction of the prognosis of AKI 4.
• The Kidney Disease Improving Global Outcomes (KDIGO) classification of AKI is based on changes in serum creatinine and urine output, but has potential pitfalls related to the fact that neither creatinine nor urine output are renal-specific 5.

Clinical Practice Guidelines for AKI

Clinical practice guidelines for AKI have been developed to standardize the diagnosis and treatment of the disorder.

• A review of major published guidelines found significant agreement among the various guidelines, but noted the limited scope of knowledge about optimal management of patients with AKI 6.
• New diagnostic tools, including novel AKI biomarkers and techniques to measure glomerular filtration rate in real time, are being developed and validated to improve the diagnosis of AKI 5.