A 35-year-old woman with a 2-week history of gross hematuria, facial puffiness, and blood pressure of 156/98 mmHg is investigated for acute glomerulonephritis. Serum creatinine is 1.8 mg/dL (baseline 0.9 mg/dL), and urine shows dysmorphic RBCs with RBC casts. Serological workup reveals elevated anti-GBM antibodies. Which of the following is NOT consistent with the diagnosis of anti-GBM disease (Goodpasture syndrome)?