A HIDA scan is an imaging test that tracks how bile moves through your liver, gallbladder, and small intestine. The name stands for hepatobiliary iminodiacetic acid, which refers to the radioactive tracer injected into your vein during the test. That tracer behaves like bile, getting absorbed by your liver and flowing through the same ducts bile normally travels. A camera follows it in real time, revealing blockages, inflammation, or a gallbladder that isn’t working properly.
What a HIDA Scan Is Used For
The most common reason for a HIDA scan is to check for gallbladder inflammation, known as cholecystitis. If the tracer flows through your liver and into your bile ducts but never fills your gallbladder, that strongly suggests acute cholecystitis, meaning the gallbladder is blocked and inflamed. The scan can also detect bile duct obstructions, bile leaks after surgery, congenital problems in the bile ducts (such as biliary atresia in infants), and complications following a liver transplant.
Your doctor may also order a version of this test specifically to measure how well your gallbladder squeezes and empties, a measurement called gallbladder ejection fraction. This is particularly useful for diagnosing biliary dyskinesia, a condition where the gallbladder looks structurally normal on ultrasound but doesn’t contract well enough to push bile out. If tracer is detected outside the biliary system entirely, that points to a bile leak.
How the Scan Works
You’ll lie on your back on an exam table, and a nurse or technologist will place an IV line in your hand or arm. The radioactive tracer is injected through the IV, and a gamma camera positioned over your abdomen starts capturing images immediately. During the first minute, the camera takes rapid one-second frames to watch the tracer enter your liver. Then it switches to one-minute frames for the next hour, building a detailed picture of how the tracer moves from your liver into your bile ducts, gallbladder, and eventually your small intestine.
At the one-hour mark, you may be repositioned for additional views from different angles. These help distinguish between the gallbladder, the common bile duct, and the opening into the small intestine, which can look similar from a single angle.
When Extra Steps Are Needed
If the gallbladder hasn’t filled with tracer after one hour, that doesn’t necessarily end the test. A common next step is an injection of morphine at a low dose. This causes a small muscle at the base of the bile duct to tighten, redirecting incoming bile toward the gallbladder. In a healthy gallbladder, tracer begins appearing within 5 to 10 minutes of the morphine injection and fills completely within 30 minutes. This approach keeps the total exam time to about 90 minutes.
For patients with significant liver disease, the liver may process the tracer much more slowly. In those cases, you might need to return for follow-up images up to 24 hours later.
Measuring Gallbladder Ejection Fraction
When the goal is to evaluate how well your gallbladder contracts, the test includes an injection of a synthetic hormone called sincalide. This mimics the natural hormone your body releases after eating, which triggers gallbladder contraction. Sincalide is given slowly over 10 minutes (a slower infusion reduces nausea), and the camera records one-minute frames for the following hour to track how much tracer leaves the gallbladder.
The result is your gallbladder ejection fraction: the percentage of tracer that gets squeezed out. A normal ejection fraction is generally 38% or higher. An ejection fraction below 35% is the most widely used threshold for diagnosing biliary dyskinesia. A low number indicates the gallbladder’s muscular wall isn’t contracting strongly enough to empty bile efficiently, which can cause recurring pain, nausea, and bloating even when no gallstones are present.
How to Prepare
You’ll need to fast for 4 to 5 hours before the scan. This is important because eating triggers your gallbladder to contract and release bile. If your gallbladder has already emptied before the test starts, the tracer won’t fill it properly, and the results will be unreliable.
Fasting too long is also a problem. If you haven’t eaten in more than 12 hours, your gallbladder may be overly full of thick, concentrated bile that prevents the tracer from entering. In that situation, you may be asked to eat a small meal first and then fast for another 4 to 5 hours before the scan begins. Certain medications, particularly opioid pain relievers, can also affect bile duct function and may need to be paused beforehand. Your care team will give you specific instructions.
What to Expect During the Test
The scan itself is painless beyond the initial IV stick. You’ll wear a hospital gown and lie still on the exam table while the camera captures images. You don’t go inside a tube like an MRI. The camera sits close to your abdomen but doesn’t touch you. Most people find the experience boring rather than uncomfortable.
A standard HIDA scan takes one to four hours depending on how quickly the tracer moves and whether additional steps like morphine or sincalide injections are needed. If sincalide is used, some people experience brief nausea or mild cramping as the gallbladder contracts, but this typically passes within minutes. The radioactive tracer leaves your body naturally through urine and stool over the following day or two.
What the Results Mean
Results are based on where the tracer goes and how quickly. A normal scan shows the tracer moving smoothly from the liver into the bile ducts, filling the gallbladder, and then draining into the small intestine. Deviations from that pattern point to specific problems.
- Gallbladder never fills with tracer: This is the hallmark finding of acute cholecystitis. It means the duct leading to the gallbladder is blocked, usually by a gallstone.
- Low ejection fraction (below 35%): Suggests chronic cholecystitis or biliary dyskinesia. The gallbladder fills but doesn’t contract well enough to empty.
- Tracer doesn’t reach the small intestine: Points to a blockage in the common bile duct, potentially from a gallstone, stricture, or tumor.
- Tracer appears outside the biliary system: Indicates a bile leak, which is most commonly seen after gallbladder surgery or abdominal trauma.
Your results will typically be interpreted by a radiologist or nuclear medicine specialist and sent to the doctor who ordered the test. In many cases, the HIDA scan provides the definitive answer when an ultrasound has already shown a normal-looking gallbladder but symptoms persist. It’s especially valuable for catching functional problems that structural imaging simply can’t detect.