How do we diagnose acute kidney injury on top of chronic kidney disease?

From the Guidelines

Diagnosing acute kidney injury (AKI) on top of chronic kidney disease (CKD) requires careful assessment of changes in kidney function from the patient's baseline, with the diagnosis made when there is an abrupt decline in kidney function, typically defined as an increase in serum creatinine by ≥0.3 mg/dL within 48 hours, or a ≥50% increase from baseline within 7 days, or a reduction in urine output to <0.5 mL/kg/hour for 6 hours, as stated in the KDIGO guidelines 1. The diagnosis of AKI on CKD is challenging because CKD patients have reduced renal reserve and may show smaller absolute increases in creatinine despite significant kidney injury. Additionally, their baseline creatinine is already elevated, making percentage-based changes more meaningful than absolute values. Early recognition is critical as AKI on CKD carries higher morbidity and mortality than either condition alone. Diagnostic workup should include comprehensive laboratory tests (complete blood count, comprehensive metabolic panel, urinalysis), assessment of urine output, and possibly renal ultrasound to rule out obstruction, as recommended by the American College of Radiology 1. Careful medication review is crucial to identify nephrotoxic agents. It's essential to compare current values to their stable baseline rather than to normal reference ranges, and to differentiate between progression of chronic disease and acute injury, as stated in the KDOQI US commentary on the 2012 KDIGO clinical practice guideline for the evaluation and management of CKD 1. The use of validated prediction models for progression of kidney disease may be able to incorporate numerous clinical factors and provide a single prognostic metric, which can guide decisions, as mentioned in the KDOQI US commentary 1. The ESPEN guideline on clinical nutrition in hospitalized patients with acute or chronic kidney disease also provides useful information on the diagnosis and management of AKI on CKD 1. Overall, diagnosing AKI on CKD requires a comprehensive approach, taking into account the patient's baseline kidney function, clinical presentation, and laboratory results, as well as careful consideration of potential nephrotoxic agents and other factors that may contribute to kidney injury.

Some key points to consider when diagnosing AKI on CKD include:

• The KDIGO definition of AKI, which includes an increase in serum creatinine by ≥0.3 mg/dL within 48 hours, or a ≥50% increase from baseline within 7 days, or a reduction in urine output to <0.5 mL/kg/hour for 6 hours 1
• The importance of comparing current values to the patient's stable baseline rather than to normal reference ranges 1
• The need to differentiate between progression of chronic disease and acute injury 1
• The use of comprehensive laboratory tests, assessment of urine output, and possibly renal ultrasound to rule out obstruction 1
• The importance of careful medication review to identify nephrotoxic agents
• The use of validated prediction models for progression of kidney disease to guide decisions 1

From the Research

Diagnosing Acute Kidney Injury on Top of Chronic Kidney Disease

To diagnose acute kidney injury (AKI) on top of chronic kidney disease (CKD), several factors and tests are considered:

• Definition and Classification: AKI is characterized by an abrupt decline in glomerular filtration rate, leading to the accumulation of urea and other chemicals in the blood 2. It is classified according to the RIFLE criteria, which consider changes in serum creatinine or urine output.
• Diagnostic Evaluation: The diagnostic evaluation for AKI includes a patient history to identify nephrotoxic medication use or systemic illnesses, physical examination to assess intravascular volume status, and laboratory tests such as serum creatinine level, complete blood count, urinalysis, and fractional excretion of sodium 3.
• Risk Factors: Recognition of risk factors for AKI, including older age, sepsis, hypovolemia/shock, cardiac surgery, infusion of contrast agents, diabetes mellitus, preexisting CKD, cardiac failure, and liver failure, is crucial for early diagnosis and management 3.
• Ultrasonography: Ultrasonography of the kidneys is recommended to rule out obstruction, particularly in older men 3.
• Medication-Induced AKI: Certain medications, such as diuretics, angiotensin-converting enzyme inhibitors, and antibiotics, can increase the risk of AKI, and their administration should be carefully considered in patients with CKD 4.
• Integrated Clinical Syndrome: The distinction between AKI and CKD may be artificial, and consideration should be given to the integrated clinical syndrome of diminished glomerular filtration rate, with acute and chronic stages 5.

Key Considerations

When diagnosing AKI on top of CKD, it is essential to:

• Monitor serum creatinine levels and urine output closely
• Assess for risk factors and potential causes of AKI
• Use ultrasonography to rule out obstruction
• Be cautious with medication administration, particularly with potentially nephrotoxic drugs
• Consider the integrated clinical syndrome of diminished glomerular filtration rate, with acute and chronic stages 5