A patient is supposed to fast for 8 to 12 hours ahead of an abdominal ultrasound, according to Mayo Clinic. The fast includes complete avoidance of any food and liquids. It is sometimes permissible to drink water, but a patient should discuss this with a doctor in advance.
The primary goal of an ultrasound on the abdomen is to get a clear picture of the aorta. Having food or liquids in the stomach or urine in the bladder can impede the technician's view, according to Mayo Clinic. A patient on medications should talk to a doctor about whether these are allowed while fasting.