A 58-year-old man is admitted for acute kidney injury. His serum creatinine has risen from a baseline of 1.0 mg/dL to 3.5 mg/dL over 48 hours. Urine dipstick shows 3+ protein and 3+ blood. Urine microscopy reveals dysmorphic red blood cells and red blood cell casts. Which of the following is the most likely diagnosis?

The correct answer to the question "A 58-year-old man is admitted for acute kidney injury. His serum creatinine has risen from a baseline of 1.0 mg/dL to 3.5 mg/dL over 48 hours. Urine dipstick shows 3+ protein and 3+ blood. Urine microscopy reveals dysmorphic red blood cells and red blood cell casts. Which of the following is the most likely diagnosis?" is Option C: Glomerulonephritis.

The other options — A) Prerenal azotemia, B) Acute tubular necrosis, D) Postrenal obstruction — are incorrect for this USMLE Exam Prep question. As explained above: The presence of dysmorphic red blood cells and red blood cell casts on urine microscopy, along with significant proteinuria and hematuria, is highly suggestive of acute glomerulonephritis.