a 38-year-old man without a significant medical history presents for an evaluation due to 1 year of diarrhea associated with cramping. he reports large volume, nonbloody, and greasy stools and he’s unintentionally lost more than 20lb. he’s also had intermittent patchy rashes to his elbows, knees, and abdomen which he states is itchy. he’s tried eliminating dairy from his diet but without any improvement. he denies fever or other constitutional symptoms. he does not know his family history due to being adopted. on exam the only significant findings are some glossitis and a papulovesicular eruption to the elbows, knees, and abdomen with some excoriations. what is the best diagnostic test to confirm this patient’s suspected diagnosis?
