What is the initial workup for a patient suspected of having Acute Kidney Injury (AKI)?

From the Guidelines

The initial workup for a patient suspected of having Acute Kidney Injury (AKI) should include a comprehensive assessment of history, physical examination, laboratory tests, and imaging studies, as outlined in the most recent guidelines 1. Begin with a detailed history focusing on potential causes such as recent medication changes (especially NSAIDs, antibiotics, contrast agents), volume status, recent illnesses, or surgeries. Physical examination should assess volume status, vital signs, and signs of systemic disease. Laboratory tests should include serum creatinine and blood urea nitrogen (BUN) to confirm AKI (typically defined as a rise in creatinine by ≥0.3 mg/dL within 48 hours or ≥50% increase from baseline within 7 days), complete blood count, comprehensive metabolic panel, and urinalysis with microscopy. Some key points to consider in the workup include:

• Urine studies should include urine sodium, creatinine, protein, and osmolality to help differentiate between prerenal, intrinsic, and postrenal causes.
• Calculate the fractional excretion of sodium (FENa) to distinguish prerenal (FENa <1%) from intrinsic renal causes (FENa >2%).
• Renal ultrasound is essential to rule out obstruction and assess kidney size and echogenicity.
• Additional tests may include specific autoimmune markers, complement levels, or renal biopsy depending on the suspected etiology, as suggested by recent studies 1. This systematic approach helps identify the cause of AKI, which is crucial for appropriate management and preventing further kidney damage. It is also important to note that the management of AKI should be tailored to the individual patient, taking into account their underlying medical conditions and the severity of the AKI, as recommended by recent guidelines 1.

From the Research

Initial Workup for Acute Kidney Injury (AKI)

The initial workup for a patient suspected of having Acute Kidney Injury (AKI) involves several key components, including:

• Patient history to identify the use of nephrotoxic medications or systemic illnesses that might cause poor renal perfusion or directly impair renal function 2
• Physical examination to assess intravascular volume status and identify skin rashes indicative of systemic illness 2
• Laboratory evaluation, including:
  • Measurement of serum creatinine level 2, 3, 4
  • Complete blood count 2
  • Urinalysis 2, 4
  • Fractional excretion of sodium 2
• Ultrasonography of the kidneys to rule out obstruction, particularly in older men 2
• Assessment of volume status, including the use of central venous and arterial blood pressure monitoring and inferior vena cava echocardiography 4
• Point-of-care ultrasonography (POCUS) to aid in excluding hydronephrosis and providing real-time insights into hemodynamics 5

Classification of AKI

The diagnostic evaluation can be used to classify AKI as prerenal, intrinsic renal, or postrenal 2, 6, 3. This classification is important for guiding treatment and management.

Key Considerations

The initial workup should also consider the patient's risk factors for AKI, including older age, sepsis, hypovolemia/shock, cardiac surgery, infusion of contrast agents, diabetes mellitus, preexisting chronic kidney disease, cardiac failure, and liver failure 2. A team-based approach to prevention, early diagnosis, and aggressive management is critical for improving outcomes 2.