Q. A 55-year-old male with a past medical history of hypertension and type 2 diabetes presents to the emergency department with nausea, vomiting, and decreased urine output. He reports not having urinated in the past 12 hours. The patient denies any fevers or known sick contacts. He smokes 1 pack of cigarettes per day, and drinks “a few beers” every night. His current medications include lisinopril, metformin, and glipizide. On physical examination, he is afebrile and appears weak. No rashes or lesions are detected. His blood pressure is 156/96 mm Hg, heart rate 110/min, respiratory rate 20/min, and oxygen saturation is 98 percent on room air. His neck is supple and there is no jugular venous distention. Auscultation of his chest reveals clear breath sounds bilaterally, and his cardiac assessment demonstrates regular rate and rhythm, with no murmurs, rubs, or gallops. His abdomen is soft, nontender, and without organomegaly. No peripheral edema is appreciated. You order a urinalysis and bloodwork. Laboratory results reveal a creatinine of 2.3 mg/dL, BUN 70 mg/dL, and urine specific gravity of 1.010. Based on your findings, including the buildup of nitrogenous waste products, you suspect a decreased glomerular filtration rate. Which of the following findings is most supportive of a prerenal cause of this patient’s azotemia?