A 22-year-old man comes to the physician for a 3-month history of intermittent abdominal pain and bloody stools. He believes he may have lost around 5 pounds over this time. He reports occasional low-grade fevers and fatigue. He also noticed a painful red bump on his shin that appeared a few weeks ago and has not gone away. Physical examination reveals mild RLQ abdominal tenderness and an erythematous left shin. Hemoglobin is 10 g/dL. MCV is 85 fL. His mother has psoriasis. Which of the following is the most appropriate next step in confirming the diagnosis?
A) Abdominal CT scan
B) Anti-saccharomyces cerevisiae antibody testing
C) Colonoscopy
D) HLA-B27 testing
E) Small bowel capsule endoscopy
