The influence of fasting on abdominal ultrasound image quality - a randomized controlled trial.

Background: Many patients are instructed to fast before abdominal ultrasound examinations in order to obtain better image quality. However, the few available studies on this topic have so far failed to demonstrate an advantage of several hours of fasting. Prolonged fasting can lead to patient distress, hypoglycemia (e.g. in insulin-treated patients), and malnutrition. Therefore, unnecessary fasting should be avoided.

Methods: For this prospective investigator-blinded study, we recruited 250 inpatients who were registered for abdominal ultrasonography in our hospital and randomized them into one of three groups: fasting for several hours, regular breakfast, or a liquid oral nutritional supplement. 215 patients could be evaluated. The sonographies were performed consecutively by inexperienced and experienced examiners who independently rated the image quality of seven anatomical structures (gallbladder, common hepatic duct [i.e., proximal part of the common duct], common bile duct [i.e., distal part of the common duct], pancreatic head, pancreatic body, pancreatic tail, and origin of the superior mesenteric artery) on a Likert scale from 1 to 5. The mean of these scores was calculated as a parameter for the diagnostic quality of the abdominal ultrasound examination.

Results: No significant difference was found for sonographic image quality after eating breakfast vs. fasting in both experienced and inexperienced examiners. In inexperienced examiners, image quality was rated slightly better after intake of liquid nutritional supplements compared to a normal breakfast (p = 0.023) or fasting (p = 0.047). However, the effect size was small.

Conclusion: A general recommendation for several hours of fasting before abdominal sonography is not necessary.