Fasting before elective abdominal ultrasound: a systematic review and meta-analysis

Fasting before elective abdominal ultrasound is widely recommended to improve image quality or visualization of abdominal structures although supporting evidence is limited. We examined whether fasting is associated with improved diagnostic or image quality-related outcomes in adult abdominal ultrasound. We conducted a systematic review and meta-analysis (PROSPERO CRD42024568514) of studies comparing fasting and non-fasting conditions in adults undergoing elective abdominal ultrasound (search date July 18, 2025; 5 databases). Study quality and risk of bias were assessed, and randomized trials were pooled using random effects models. Real-world preparation recommendations were evaluated across international ultrasound society guidelines and patient-facing sources. 14 studies (9 randomized trials, 5 observational studies; 2,208 participants) met the inclusion criteria. Five randomized trials were eligible for meta-analysis; three were included in the primary analysis (n = 378). Two trials contributed organ-specific outcomes to sensitivity analyses. Fasting did not improve overall diagnostic sufficiency, defined as adequate visualization to answer the clinical question without repeat imaging (OR 0.97, 95% CI 0.51-1.86, p = 0.92; I² = 0%). Significant effects were limited to gallbladder visibility and detectability of the common bile duct, with no consistent benefit otherwise. Risk of bias was moderate and overall certainty of evidence was low. Real-world fasting instructions were highly variable and rarely evidence-based. Fasting before elective abdominal ultrasound does not improve diagnostic sufficiency. Observed benefits were limited to the biliary tract. Given the low certainty of evidence and limited observed benefits beyond the biliary tract, strict and prolonged fasting recommendations should be reconsidered.