Review Question - QID 213864

A 2-year-old boy is brought to the emergency department by his parents after they found a maroon-colored stool in his diaper. He is in no acute distress and has been tolerating feeds with regular bowel movements and no vomiting. He has been afebrile and remains playful. His parents also noticed a maroon-colored stool 2 weeks ago. His temperature is 98.2°F (36.8°C), blood pressure is 95/50 mmHg, pulse is 105/min, and respirations are 24/min. On physical exam, his heart rate and rhythm are regular, and his lungs are clear to auscultation bilaterally. His abdomen is slightly distended, and there is mild tenderness to palpation in the right lower quadrant. Laboratory results are shown below:

Hemoglobin: 12.2 g/dL
Hematocrit: 44%
Leukocyte count: 10,000/mm^3 with normal differential
Platelet count: 150,000/mm^3
Heme occult stool testing: Positive
Fecal leukocytes: Negative

Which of the following tests will most likely confirm this patient's diagnosis?