An 88-year-old woman with Alzheimer disease is brought to emergency because of fever and chills for 2 days. Temperature is 102 F. Physical examination demonstrates left costovertebral angle tenderness. Laboratory studies show:
Serum WBC 15,000/μL
Urine RBC 1+
Urine WBC 1+
Urine bacteria Few
Urine granular casts Many
Which of the following is the most likely explanation for these findings?
Interstitial nephritis
Membranous glomerulonephritis
Proliferative glomerulonephritis
Pyelonephritis
Tubular necrosis
