A 42-year-old man presents with lower extremity swelling. His examination is only remarkable for 2+ pitting edema in the lower extremities. The patient is counseled on a low-salt diet. The abnormal laboratory values are as follows: 3+ protein, coarse granular casts, 2-5 WBCs, 0-2 RBCs, Serum albumin 2.1 gm/dL, Serum creatinine 2.0 mg/dL, Serum BUN 18 mg/dL, Hemoglobin 12.1 gm/dL. What is the next best step in treatment?
a) Initiate corticosteroid therapy
b) Refer the patient to a nephrologist for further evaluation
c) Start antihypertensive medication
d) Begin dialysis