A 50-year-old woman presents to her physician because she has not been feeling well for the past 2 to 3 weeks. She has generalized malaise and a nagging cough that occasionally produces blood-tinged...

Explain.

Extracted text: A 50-year-old woman presents to her physician because she has not been feeling well for the past 2 to 3 weeks. She has generalized malaise and a nagging cough that occasionally produces blood-tinged sputum. Today, for the first time, she noticed dark-colored urine. Physical examination reveals an ill-appearing middle-aged woman with a blood pressure of 180/110 mm Hg. Diminished air entry in the lungs bilaterally and an ulcerated lesion of the mucosa of the right naris are noted. The patient has no history of asthma or allergies. Urinalysis is grossly positive for blood, and a serum chemistry panel reveals a creatinine level of 1.7 mg/dL. What additional finding would confirm the most likely diagnosis?