A 45-year-old man with diabetes mellitus presents with recurrent episodes of pyelonephritis. Imaging reveals scarring and atrophy of the renal parenchyma. Which of the following is the most likely complication if this condition remains untreated?

A 26-year-old woman presents to the emergency department with complaints of fever, chills, and severe left-sided flank pain for the past 48 hours. She reports associated urinary symptoms, including dysuria, urgency, and frequency, that started a week ago. She denies vaginal discharge or abdominal pain. Her medical history is significant for recurrent UTIs, with two similar episodes in the past year. She is sexually active and uses spermicides as contraception. On examination, her temperature is 39.2°C (102.6°F), heart rate is 110 bpm, and blood pressure is 100/70 mmHg. She appears visibly uncomfortable, and palpation of the left costovertebral angle (CVA) elicits significant tenderness. Abdominal examination is unremarkable. Which of the following findings is most specific for acute pyelonephritis in this patient?

A 32-year-old woman presents to the emergency department with fever, chills, dysuria, flank pain, and nausea for 2 days. Physical examination reveals significant tenderness over the costovertebral angle (CVA). Urinalysis shows pyuria and positive nitrites. What is the next best step in the management of this patient?