Why do patients have to fast for abdominal sonograms? Patients scheduled for abdominal sonograms are instructed to have nothing to eat or drink for eight hours prior to their exam and are offered early morning appointments. Necessary medications may be taken with a sip of water.
Fasting ensures the gallbladder will be distended and also minimizes intestinal gas, which interferes with imaging abdominal organs. After eating, the gallbladder contracts, making it difficult to visualize small stones and wall thickening may be indistinguishable from cholecystitis.
So, for best results, patients should fast before abdominal sonograms. Emergencies do occur and we can attempt the scan if the patient has eaten, but if results are equivocal the scan may have to be repeated.