What is the appropriate workup for a patient with elevated creatinine (Impaired renal function)?

Workup for Elevated Creatinine (Impaired Renal Function)

The appropriate workup for elevated creatinine should include thorough laboratory testing, urinalysis, imaging, and potential specialist referral based on the severity and suspected etiology of renal impairment.

Initial Assessment

• Determine if the renal impairment is acute or chronic by reviewing previous creatinine values and calculating the rate of change 1, 2
• Categorize the cause as prerenal (impaired blood flow), intrinsic renal (parenchymal damage), or postrenal (obstruction) 1, 3
• Calculate estimated GFR using validated equations (CKD-EPI or MDRD) rather than relying on serum creatinine alone, especially in elderly patients or those with reduced muscle mass 2, 4
• Assess for signs and symptoms of uremia, fluid overload, or electrolyte disturbances 1

Laboratory Evaluation

• Complete blood count to assess for anemia, which commonly accompanies chronic kidney disease 2
• Comprehensive metabolic panel including electrolytes, BUN, and creatinine 1
• Urinalysis with microscopic examination for casts, cells, and crystals 1
• Urine albumin-to-creatinine ratio (UACR) to quantify proteinuria 1, 2
• Urine sodium and urea to help differentiate prerenal from intrinsic causes 1
• Consider specialized urinary biomarkers in selected cases 1

Imaging Studies

• Renal ultrasonography should be performed in all patients with new or worsening renal impairment to evaluate kidney size, echogenicity, and rule out obstruction 1, 2
• Consider additional imaging based on clinical suspicion:
  • CT with or without contrast (weighing risk-benefit ratio in patients with impaired renal function) 1
  • MRI without gadolinium if advanced renal impairment is present 1
  • Renal Doppler ultrasound if renovascular disease is suspected 1

Medication Review

• Identify and discontinue potentially nephrotoxic medications (NSAIDs, certain antibiotics) 1, 2
• Review medications requiring dose adjustment for renal function 2, 4
• Consider holding ACE inhibitors or ARBs temporarily if acute kidney injury is present, but do not discontinue for minor increases in serum creatinine (≤30%) in the absence of volume depletion 1, 4

Special Considerations

• For diabetic patients, optimize blood pressure control with target <140/90 mmHg to reduce risk of CKD progression 1, 2
• In patients with cirrhosis and AKI, perform diagnostic paracentesis to evaluate for spontaneous bacterial peritonitis 1
• For immune checkpoint inhibitor-related nephritis, consider renal biopsy if AKI is refractory to steroids 1

Indications for Nephrology Referral

• eGFR <30 mL/min/1.73m² 1, 2
• Rapid progression of kidney disease (sustained decrease in eGFR >20%) 2, 5
• Difficult management issues (resistant hypertension, electrolyte abnormalities) 1, 2
• Uncertainty about the etiology of kidney disease 1, 2
• Persistent significant proteinuria (UACR ≥300 mg/g) 1, 2

Common Pitfalls to Avoid

• Relying solely on serum creatinine without calculating eGFR, especially in elderly patients or those with altered muscle mass 4, 6
• Failing to identify potentially reversible causes of renal impairment 5
• Inadequate blood pressure control in patients with renal disease 7
• Delaying nephrology referral for patients with progressive renal disease 5
• Overlooking the significance of even mild elevations in serum creatinine, which can represent substantial reductions in GFR 4, 7