A 40-year-old female presented with hematuria and pain in both flanks. H/O recurrent UTI. She has swelling of both feet and facial puffiness. Her mother had a history of urinary stones and underwent a kidney transplant. Abdominal examination shows palpable, bilateral flank masses. Her serum creatinine is 2.7 mg/dL. Which of the following additional findings is seen in this patient?