What are the criteria for Acute Kidney Injury (AKI) in patients with Chronic Kidney Disease (CKD)?

From the Guidelines

The criteria for acute kidney injury (AKI) in patients with chronic kidney disease (CKD) include an increase in serum creatinine by 0.3 mg/dL or more within 48 hours, a 50% or greater increase in serum creatinine from baseline within 7 days, or urine output less than 0.5 mL/kg/hour for 6 hours or more, as defined by the KDIGO guidelines 1. For patients with CKD, the baseline creatinine is their stable pre-illness value, not an assumed normal value. This distinction is crucial because patients with CKD already have elevated baseline creatinine levels. When monitoring for AKI in CKD patients, it's essential to compare current values to their individual baseline rather than population norms. The diagnosis may be more challenging in CKD patients due to their reduced renal reserve and potentially blunted creatinine rises. Additionally, urine output criteria should be interpreted cautiously in CKD patients who may have chronically reduced urine output. Regular monitoring of creatinine, urine output, and other markers of kidney function is essential for early detection of AKI superimposed on CKD, as these patients are at higher risk for complications and progression to end-stage kidney disease, as noted in the KDIGO commentary 1. Some studies have shown that small rises in creatinine are independently associated with increased mortality, highlighting the importance of early detection and intervention 1. The KDIGO guidelines provide a framework for the diagnosis and staging of AKI, including the use of serum creatinine and urine output criteria, and are widely accepted as the standard for clinical practice 1. It's worth noting that the definition of AKI and its use in practice is still evolving, and further research is needed to refine the criteria and improve outcomes for patients with CKD and AKI 1. However, based on the current evidence, the KDIGO guidelines provide a reliable and widely accepted framework for the diagnosis and management of AKI in patients with CKD. Key points to consider when diagnosing AKI in CKD patients include:

• Using the patient's individual baseline creatinine value rather than a population norm
• Interpreting urine output criteria cautiously in patients with chronically reduced urine output
• Regularly monitoring creatinine, urine output, and other markers of kidney function
• Using the KDIGO guidelines as a framework for diagnosis and staging of AKI.

From the Research

Definition of Acute Kidney Injury (AKI) with Chronic Kidney Disease (CKD)

• AKI is characterized by an abrupt decrease in renal function or the onset of frank renal failure 2.
• 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.

Criteria for AKI with CKD

• A new AKI classification using absolute increase in SCr elevation over specified time periods has been suggested based on creatinine kinetics 3.
• The reference change value (RCV) of SCr given initial SCr level in adults without known risks of acute kidney injury other than CKD has been proposed as a criterion for acute on chronic kidney injury (ACKI) 4.
• The cROCK criterion defines ACKI as a ≥25% increase in SCr in 7 days 4.
• The KDIGO criteria and Cr kinetics criteria have been compared, and the results show that the Cr kinetics criteria can be superior when diagnosing patients with previous CKD, while KDIGO had a better performance in patients with no previous CKD 3.

Diagnosis and Management of AKI with CKD

• Determining the cause of AKI is critical when possible, and the history should focus on risk factors, including nephrotoxic drugs 2.
• The physical examination should include determination of fluid volume status, and urinalysis with microscopy can narrow the differential diagnosis 2.
• AKI management includes control of the underlying cause, achievement and maintenance of euvolemia, nutritional optimization, blood glucose control, and pharmacotherapy 2.
• Treatment with fluid resuscitation or diuresis is guided by the volume status, and emergent referral to a nephrology subspecialist is recommended for patients with stage 2 or 3 AKI 2.