A 23-year-old college student presents with 2 to 3 weeks of…
A 23-year-old college student presents with 2 to 3 weeks of frequent stools that are mixed with blood and mucus. The frequent stools are associated with worsening tenesmus. Vital signs are within normal limits, and the physical examination is normal. The white blood cell count is also normal, and stool testing for infectious agents is negative. Which one of the following is the best next step in evaluating this patient?