A 45-year-old female with systemic lupus erythematosus presents with lower extremity edema and new-onset hypertension. Urinalysis reveals 4+ protein, microscopic hematuria, and red blood cell casts. Serum creatinine has risen from 0.8 to 2.1 mg/dL. What diagnostic procedure is essential to guide immunosuppressive therapy?

Answer and explanation

Correct answer: B. Percutaneous renal biopsy

  1. Step 1: Evaluate clinical findings: Active nephritic-nephrotic syndrome with red cell casts and rapid renal impairment in a patient with SLE strongly indicates active lupus nephritis.
  2. Step 2: Identify treatment prerequisites: Classification of lupus nephritis (Classes I through VI according to ISN/RPS criteria) dictates therapy (e.g., pulse steroids and mycophenolate mofetil/cyclophosphamide for Class III/IV).
  3. Step 3: Confirm required test: Percutaneous renal biopsy is necessary for histological classification and activity/chronicity scoring.
Answer
Percutaneous renal biopsy.
Why not the others: 'Abdominal CT' evaluates gross anatomy but carries contrast nephropathy risk and cannot assess glomerular histology; 'Retrograde pyelography' evaluates ureteric obstruction; 'Metanephrines' screens for pheochromocytoma.

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