A 65-year-old man presents to the emergency room with complaints of weakness, generalized swelling in his extremities, and right leg pain. At the time of presentation, he appears to be in moderate distress from the leg pain. The patient states that his symptoms started two days ago. The patient also has frequent urination and increased thirst. He states that he has felt weak for the past few months. Physical examination reveals a tender, erythematous, and swollen right calf. He also has 2+ pitting edema in all extremities. Blood pressure is 107/55 mm Hg, and temperature is 100.3 F. Venous ultrasound is positive for lower extremity deep vein thrombosis. Laboratory studies reveal:
White cell count 11,000/mm3; hematocrit 32.3%; platelets 105,000/mm3; K 4.0 mEq/L; BUN 24 mg/dL; creatinine 1.7 mg/dL. The PT/PTT are normal.
Total bilirubin 0.4 mg/dL, AST 28 U/L, albumin l.9 g/dL, cholesterol 326 mg/dL; triglycerides 425 mg/dL.
Urine dipstick shows protein 3+, hemoglobin 1+, white cells 1+; 24-hour urine shows 6.2 grams of protein.
What is the next step in the treatment of this patient?
(A) Renal biopsy