A 25-year-old man comes to your clinic complaining of abdominal pain for the past two days. Yesterday, the pain was periodic and located around the periumbilical area. Today the pain is persistent and located in the right lower quadrant. He feels feverish. He does not smoke or drink alcohol. His body temperature is 37.7℃, blood pressure is 126/62mmHg, and pulse rate is 94/min, regular.
Which one of the following should be done next?