Fasting Requirements for Liver Ultrasound
For standard liver ultrasound imaging, fasting is not necessary, but for liver stiffness measurements (elastography), you must fast for at least 3 hours.
Standard Liver Ultrasound (B-mode imaging)
No fasting is required for routine diagnostic liver ultrasound examination to assess liver parenchyma, detect masses, evaluate cirrhosis, or visualize liver anatomy 1, 2.
A randomized controlled trial of 215 patients demonstrated no significant difference in image quality between patients who fasted for several hours versus those who ate a regular breakfast 1.
Another prospective randomized study of 150 patients confirmed that technical success of abdominal ultrasound did not differ between fasting and non-fasting groups 2.
Unnecessary fasting causes patient distress, risk of hypoglycemia (particularly in insulin-treated patients), and potential malnutrition, which should be avoided 1.
Liver Stiffness Measurement (Elastography)
If your ultrasound includes elastography techniques (transient elastography/FibroScan, shear wave elastography, or MRE), you must fast for a minimum of 3 hours 3.
Meal ingestion increases liver stiffness values regardless of the measurement method used, which can lead to overestimation of fibrosis and misdiagnosis 3.
The European Association for the Study of the Liver (EASL) guidelines specifically state that while 2 hours fasting was previously recommended, studies have shown that return to normal values requires at least 3 hours 3.
This 3-hour fasting requirement applies to all elastography methods: vibration controlled transient elastography (VCTE/FibroScan), point-shear wave elastography (pSWE), bidimensional shear wave elastography (2D-SWE), and magnetic resonance elastography (MRE) 3.
Special Considerations for Doppler Ultrasound
For hepatic artery Doppler evaluation in liver transplant patients, fasting is recommended because meal ingestion significantly alters hepatic arterial hemodynamics, decreasing arterial blood flow and increasing resistive index 4.
In pediatric liver transplant patients undergoing routine portal vein Doppler surveillance, fasting may not be necessary as measurements show good consistency pre- and postprandially 5.
Practical Recommendations
Ask your ordering physician what type of liver ultrasound you're having: standard imaging only, or if it includes elastography/stiffness measurement 3.
If elastography is included, fast for at least 3 hours (water is typically allowed) 3.
If only standard B-mode ultrasound imaging is ordered, you may eat normally before the examination 1, 2.
For liver transplant Doppler studies, follow your transplant center's specific protocol, as fasting may be required for accurate hepatic artery assessment 4.