Interpretation of the renal biopsy

An 84-year-old female with a history of hypertension presents to the emergency department complaining of shortness of breath. On exam, blood pressure is 180/90 mmHg. Cardiac exam is normal, breath sounds are diminished in both lung bases, and +2 pitting edema is present. Chest X-ray reveals bilateral pleural effusions, and she is hospitalized for suspected acute congestive heart failure. Serum creatinine is elevated to 1.8-1.9 mg/dL from 1.2 mg/dL measured 5 months previously. A urinalysis shows 9.9 g of total protein excretion per day, 31-40 red blood cells per high power field of which greater than 25 % were dysmorphic, 11-20 white blood cells per high power field, lipiduria, and granular casts. Nephrology is consulted. Renal ultrasound demonstrates normal sized kidneys, patent renal veins, and no evidence of hydronephrosis. Initial serologic studies are negative including antinuclear antibody, erythrocyte sedimentation rate, C-reactive protein, antibodies to hepatitis B and C viruses, anti-neutrophil cytoplasmic antibodies (ANCA), and anti-glomerular basement membrane (GBM) antibody titers. C3 is normal, and C4 is mildly reduced at 11 mg/dL (normal 14-40 mg/dL). No monoclonal protein is detected by serum or urine protein electrophoresis studies. To determine the diagnosis, a renal biopsy is recommended.