From the Guidelines
The workup of a patient with Acute Kidney Injury (AKI) should begin with a thorough history, physical examination, and basic laboratory tests to determine the cause and severity, as outlined in the most recent guidelines 1. To initiate the workup, assess volume status and hemodynamics, looking for signs of hypovolemia, heart failure, or shock. Order basic labs including serum creatinine, BUN, electrolytes, urinalysis, and urine microscopy.
- Calculate the patient's baseline GFR and determine the AKI stage using KDIGO criteria (Stage 1: 1.5-1.9x baseline creatinine; Stage 2: 2.0-2.9x baseline; Stage 3: ≥3.0x baseline) 1.
- Obtain a urine output measurement, as oliguria (<0.5 mL/kg/hr for >6 hours) suggests more severe injury.
- Categorize the AKI as prerenal (due to decreased renal perfusion), intrinsic (direct kidney damage), or postrenal (urinary tract obstruction). For prerenal causes, check orthostatic vital signs and assess response to a fluid challenge (250-500mL crystalloid).
- For intrinsic causes, order urine sodium, fractional excretion of sodium (FENa), and consider autoimmune markers, complement levels, or toxicology screens if indicated.
- For suspected obstruction, obtain renal ultrasound. Additional tests may include renal Doppler ultrasound for vascular causes, CT imaging without contrast, or kidney biopsy in unclear cases. Simultaneously, implement management strategies including discontinuing nephrotoxic medications, ensuring adequate hydration, optimizing hemodynamics, and treating the underlying cause, as recommended in the latest clinical practice update 1.
- Monitor electrolytes, acid-base status, and fluid balance closely, and consider nephrology consultation for severe AKI, rapidly worsening kidney function, or if dialysis might be needed. When AKI is diagnosed, diuretics and nonselective beta-blockers should be held, NSAIDs discontinued, the precipitating cause of AKI treated, and fluid losses replaced, administering albumin 1 g/kg/d for 2 days if the serum creatinine shows doubling from baseline 1. Urine output, vital signs, and when indicated, echocardiography or CVP (if there is a pre-existing central line) should be used to monitor fluid status.
From the Research
Workup of Acute Kidney Injury (AKI)
To work up a patient with Acute Kidney Injury (AKI), the following steps can be taken:
- Obtain a patient history to identify the use of nephrotoxic medications or systemic illnesses that might cause poor renal perfusion or directly impair renal function 2
- Perform a physical examination to assess intravascular volume status and identify skin rashes indicative of systemic illness 2
- Conduct an initial laboratory evaluation, including:
- Measurement of serum creatinine level
- Complete blood count
- Urinalysis
- Fractional excretion of sodium 2
- Perform ultrasonography of the kidneys to rule out obstruction, particularly in older men 2
Classification of AKI
AKI can be classified as prerenal, intrinsic renal, or postrenal based on the diagnostic evaluation 2. The Kidney Disease: Improving Global Outcomes (KDIGO) system for classification of AKI severity utilizes a staging schema based on relative changes in serum creatinine concentration and urine output 3, 4, 5, 6.
Diagnostic Criteria
The diagnostic criteria for AKI include:
- Changes in serum creatinine level
- Urine output
- Both serum creatinine and urine output 5
- New biomarkers for AKI may substantially aid in the risk assessment and evaluation of patients at risk for AKI 5
Management
Management of AKI involves:
- Fluid resuscitation
- Avoidance of nephrotoxic medications and contrast media exposure
- Correction of electrolyte imbalances
- Renal replacement therapy (dialysis) for refractory hyperkalemia, volume overload, intractable acidosis, uremic encephalopathy, pericarditis, or pleuritis, and removal of certain toxins 2