Is fasting a necessary preparation for abdominal ultrasound?

In a randomized, prospective study, 150 patients for abdominal ultrasound were divided into two groups of 75 patients each with instructions to fast for six hours or have normal breakfast respectively.The technical success of the abdominal ultrasound performed by radiologists blinded to the instruction did not differ significantly between the groups.It appears that routine fasting before abdominal ultrasound is not necessary.Optimum conditions for the ultrasonic examination of the abdominal organs require a fluid-filled gall bladder and as little gas in the gastrointestinal tract as possible [1]. In addition the thin patient is easier to examine than the fat patient since higher-frequency transducers can be used which improve resolution. Most ultrasound (US) departments instruct their patients to come fasting for such examinations, sometimes for as long as 12 hours, assuming that the gall bladder would otherwise be contracted and difficult to assess and that fasting patients will have less gas in the duodenum & colon. Vogel et al [1] have reported favourable results with a two-day low calorie diet, laxatives and fasting. Other groups have found gas reducing agents to be of no value [2]. Some investigations have found a barium meal or upper gastrointestinal series does not interfere with abdominal US although the US images, especially of the liver and gall bladder [3,4] were poor after barium enema.We have been unable to find any report on the technical outcome of abdominal US in non-fasting patients. Fasting may be inconvenient and even dangerous for some patients, particularly diabetics, and those having to travel a long way to the US department. The effect of fasting is compounded by waiting and some patients are psychologically affected by low blood sugar. Also, if a urinary bladder US examination is to follow an abdominal examination, it will take longer for the urinary bladder to fill in a fasting and poorly hydrated patient. Non-fasting may also be used as an