Q. A 32-year-old male presents to your clinic with a chief complaint of abdominal pain, bloating, and diarrhea that has been occurring for the past several months. The patient denies any fevers, nausea, or vomiting. He has no known sick contacts and no history of recent travel. He reports the symptoms primarily occur after meals. The patient also describes a history of similar symptoms in the past, which resolved when he avoided consuming dairy products. There is a family history of lactose intolerance, with his mother and sister also having similar symptoms. The patient has no other past medical history and does not take any medications. On physical examination, his vital signs are within normal limits, and the patient appears nontoxic. He is uncomfortable and reports mild abdominal pain and distention. His cardiopulmonary assessment is unremarkable. The patient’s abdomen is soft, with mild tenderness to deep palpation. You detect hyperactive bowel sounds. No masses or organomegaly are appreciated. There are no other significant findings on physical examination. Based on the information you have at this point in time, which of the following tests would be LEAST useful in confirming his most likely diagnosis?