Quick answer: for an ultrasound of the upper abdomen (liver, gallbladder, pancreas, kidneys, spleen, aorta), you are usually asked not to eat for several hours beforehand, commonly overnight or 6 to 8 hours, and some centers ask for up to 12. For a pelvic ultrasound, you may instead need a full bladder: drink up to six glasses of water about two hours before and do not urinate. The scan is painless, uses no radiation and usually takes about 30 minutes. Because instructions vary, follow the ones from your imaging center.
Ultrasound is one of the simplest imaging tests, but preparation makes a big difference to how clear the pictures are. In the U.S., the scan is usually performed by a sonographer, a specialist in ultrasound, and read by a radiologist.
What an abdominal ultrasound shows
Ultrasound uses sound waves, not x-rays, to create real-time images. An abdominal ultrasound looks at the:
- liver
- gallbladder and bile ducts
- pancreas
- kidneys
- spleen
- abdominal aorta and other blood vessels
It helps diagnose abdominal pain or swelling, abnormal liver tests, enlarged organs, gallstones, kidney stones and abdominal aortic aneurysm, and it can guide biopsies. A Doppler study, often part of the exam, shows blood flow through the vessels.
Ultrasound is the best test for gallstones. See [link: HIDA Scan: Preparation and What It Shows] for how gallbladder function is tested.
Why fasting matters
- The gallbladder needs to be full. After a meal it contracts and empties, so it becomes small and hard to examine, and stones can be missed.
- Less gas in the bowel. Sound waves do not travel through air or gas, so a full stomach and gassy bowel can hide organs such as the pancreas.
How to prepare: upper abdomen
- Do not eat for the number of hours your center tells you. Many centers schedule abdominal ultrasounds in the morning so you can fast overnight.
- Drinks: many centers allow small sips of water; some ask you to avoid all drinks. Avoid fizzy drinks, coffee with milk, juice and chewing gum, which can add gas or make the gallbladder contract.
- Medications: usually take them as normal with a little water, unless told otherwise.
- Diabetes: ask your doctor or the center how to manage fasting and your medications.
- Clothing: wear a two-piece outfit so you only need to lift or remove your top.
How to prepare: pelvis or kidneys and bladder
For ultrasounds of the pelvis (bladder, uterus, ovaries, prostate) and some kidney and bladder studies, a full bladder works as a window that lets the sound waves reach the organs behind it.
- Drink up to six glasses of water about two hours before the exam, or as instructed.
- Do not urinate until the scan is done, or until the sonographer tells you.
- If you are having an abdominal and a pelvic ultrasound on the same day, you may be asked to fast and drink water. Check your instructions.
From the scanner room: [TU EXPERIENCIA: los errores de preparación más frecuentes que ves en el servicio (desayunar, vejiga vacía o demasiado llena) y qué pasa cuando ocurren.]
What happens during the scan
- You lie on your back on an exam table, and may be asked to turn onto your side.
- The sonographer puts a warm, water-based gel on your belly. It helps the sound waves pass between the probe and your skin.
- The transducer, a small handheld probe, is moved over your abdomen with gentle pressure.
- You may be asked to take a deep breath and hold it, which moves organs such as the liver and gallbladder down from under the ribs.
- During a Doppler study, you may hear pulsing sounds as blood flow is measured.
The exam usually takes about 30 minutes, and more extensive exams up to an hour. Afterward, the gel is wiped off; it does not usually stain clothing. You may be asked to wait while the images are reviewed, and then you can return to normal activities and eat.
Does it hurt?
No. You feel the gel and light pressure. If an area is tender, such as an inflamed gallbladder, the pressure can be uncomfortable; tell the sonographer. A very full bladder can be uncomfortable for pelvic scans, but it is short-lived.
Is it safe?
Yes. Standard diagnostic ultrasound has no known harmful effects and uses no radiation, which is why it is used in pregnancy and in children.
Limitations
- Gas and air block sound waves, so the bowel and organs behind it can be hard to see.
- In larger patients, deeper structures are harder to image.
- If the ultrasound does not answer the question, your doctor may order a CT or MRI. See [link: Abdominal CT Scan: Preparation and What It Shows].
Results
A radiologist reviews the images and sends a signed report to your doctor, who will share the results. Sometimes the radiologist discusses the findings with you right after the exam.
Tips from the technologist
[TU EXPERIENCIA: 2-3 consejos propios. Ideas: pedir cita a primera hora, llevar algo para comer después, beber el agua de golpe en vez de a sorbos si te piden vejiga llena, avisar si no aguantas más la vejiga.]
Frequently asked questions
Can I drink water before an abdominal ultrasound?
Often small sips are allowed, but some centers ask you not to drink anything. Follow your instructions.
Why do I need a full bladder for an ultrasound?
For pelvic scans, a full bladder pushes the bowel out of the way and acts as a window to see the organs behind it.
How long does an abdominal ultrasound take?
Usually about 30 minutes; more extensive exams can take up to an hour.
Can I take my medications before an abdominal ultrasound?
Usually yes, with a little water. If you have diabetes, ask for specific instructions.
Can I have an abdominal ultrasound if I’m pregnant?
Yes. Ultrasound uses no radiation and is considered safe.
This article is for general information and does not replace advice from your doctor or imaging center.