An ultrasound scan uses sound waves to obtain internal images of the body. In some ultrasound examinations, such as the abdominal and pelvic scans, you require preparation before the scan. In other scans, however, such as the breast, hernia and shoulder scans, no preparation is required. Our clients regularly ask us why they need to prepare.
The main ultrasound examinations that need preparation are the abdominal scan, urinary tract and pelvic scan.
For the abdominal scan, you need to fast for at least four hours. In some Private Ultrasound clinics and in the NHS you require fasting for at least six hours. There is widespread inaccurate information online regarding the length of fasting for an abdominal scan. For example, Healthline recommends 12 hours of fasting which is nothing more than outdated, cruel and unnecessary.
The main reason for fasting for the abdominal scan preparation is to give time for the gallbladder to fill up with bile and expand, so it is visible during the ultrasound scan examination. The gallbladder is like a balloon and stores the bile. When you eat something fatty, the gallbladder excretes the bile into the bowel to break down the fat, so it collapses and therefore is difficult to be visualized on ultrasound.
Is fasting necessary for an ultrasound?
Depends on the kind of ultrasound scan. If the doctor were to exclude a gallbladder abnormality, at least four hours of fasting is necessary. If you fail to fast, your gallbladder will be deflated, and the sonographer will be able to clearly see inside the gallbladder lumen to exclude or confirm gallstones. A deflated gallbladder will also raise the possibility of a functioning problem.
If however, the scan is to merely check your liver, let's say for example to exclude or confirm fatty liver or cirrhosis, failing to fast will not affect the diagnosis.
Can I drink water before an abdominal ultrasound?
Yes, you can drink as much water as you like.
Is it OK to drink coffee before an ultrasound?
You can have black coffee or tea (no milk). You should, however, avoid fizzy drinks as these increase the amount of abdominal gas.
For the transabdominal pelvic scan, you are required to have your bladder full. The reason for this is that, as your bladder is anterior to your uterus and ovaries, it is being used as an acoustic window (a window to see through). When your bladder is full, will push out of the way the bowel that can obscure your uterus and ovaries.
This is the same reason that you have to fill up your bladder during the early pregnancy scan.