A nuclear medicine hepatobiliary scan, commonly called a HIDA scan, is an imaging test that tracks how bile flows from your liver through your gallbladder and into your small intestine. A small amount of radioactive tracer is injected into a vein, picked up by your liver cells, and excreted into bile, just like the natural waste product bilirubin. A specialized camera then follows that tracer in real time, revealing blockages, inflammation, or leaks anywhere along the biliary system.
The name “HIDA” comes from the original tracer compound (hepatobiliary iminodiacetic acid), though newer, more effective versions of the tracer are used today. You may also see it called cholescintigraphy or hepatobiliary scintigraphy. Regardless of the name, the test works the same way.
How the Tracer Works
The tracer is a technetium-99m compound that your liver cells absorb through the same transport system they use for bilirubin. Unlike bilirubin, the tracer passes through without being chemically altered, which means it stays detectable by the camera as it moves through your bile ducts, into your gallbladder, and eventually into your small intestine. This gives doctors a live map of bile flow that no other imaging test can provide as clearly.
Older versions of the tracer produced poor images when bilirubin levels in the blood were elevated above 5 mg/dL. The current tracers (disofenin and mebrofenin) are extracted far more efficiently and can still produce diagnostic images even when bilirubin levels reach 20 to 30 mg/dL. That matters because many patients needing this scan already have liver or biliary problems that raise bilirubin.
What Conditions It Diagnoses
The HIDA scan is most commonly ordered when a doctor suspects a gallbladder problem, but it evaluates the entire chain of bile production and drainage. The main conditions it can identify include:
- Acute cholecystitis: sudden gallbladder inflammation, usually from a stone blocking the duct that connects the gallbladder to the rest of the biliary system
- Chronic cholecystitis: long-term gallbladder dysfunction where the organ doesn’t contract and empty properly
- Biliary atresia: a condition in newborns where bile ducts are absent or blocked, preventing bile from reaching the intestine
- Biliary leak: bile escaping outside its normal pathway, often after surgery
- Sphincter of Oddi dysfunction: a problem with the valve that controls bile release into the small intestine
- Biliary stent patency: checking whether a previously placed stent is still open and working
The scan is particularly valuable for diagnosing acute cholecystitis because ultrasound, while good at finding gallstones, can’t always confirm whether a stone is actually blocking the cystic duct. The HIDA scan answers that question directly.
What Happens During the Scan
You’ll need to fast for at least four hours before the test. Fasting too long (more than 24 hours) can also be a problem because the gallbladder may become too full of concentrated bile, which can interfere with tracer uptake. Opioid medications like morphine and codeine need to be stopped at least six hours beforehand, as they affect the valve that releases bile into the intestine.
The procedure itself starts with a single IV injection of the tracer into your arm. You then lie on a table under a gamma camera, which captures images of the tracer as it moves through your system. The camera doesn’t emit radiation; it only detects the low-level gamma rays coming from the tracer already inside you.
A standard HIDA scan takes one to four hours. The variability depends on how quickly the tracer moves through your system and what your doctor is looking for. In some cases, you may need to return for follow-up images up to 24 hours later if the tracer moves slowly.
The Gallbladder Contraction Phase
If your doctor wants to measure how well your gallbladder empties, the technologist will inject a hormone called sincalide partway through the scan. Sincalide triggers your gallbladder to contract, and the camera measures how much tracer leaves the gallbladder compared to how much was there before. This ratio is your gallbladder ejection fraction, the single most important number from the test when chronic gallbladder disease is suspected.
How Results Are Interpreted
A normal scan shows the tracer moving smoothly from the liver into the bile ducts, filling the gallbladder, and then appearing in the small intestine within about an hour. Deviations from this pattern tell a specific story.
If the gallbladder never fills with tracer, it strongly suggests acute cholecystitis. In one study, every patient whose gallbladder failed to visualize on the scan turned out to have cholecystitis confirmed at surgery. A gallbladder that fills normally rules out cystic duct obstruction and, with it, acute cholecystitis.
Slow tracer movement through the system can point to a partial blockage or reduced liver function. If no tracer reaches the small intestine at all, the problem is likely a complete obstruction further down the biliary tree, or in infants, biliary atresia. Tracer appearing outside the normal bile pathways signals a biliary leak.
Gallbladder Ejection Fraction
For chronic gallbladder problems, the ejection fraction is the key measurement. A normal value is generally 38% or higher, meaning the gallbladder empties at least 38% of its contents when stimulated. Some studies use a slightly lower cutoff of 35%. A low ejection fraction, combined with symptoms like pain after eating fatty meals, often supports the decision to remove the gallbladder surgically.
It’s worth noting that ejection fraction alone doesn’t always predict whether surgery will relieve symptoms. Some patients with a normal ejection fraction still have gallbladder pathology found during surgery, and some with low numbers feel no better after removal. The result is most useful when it fits with your symptoms and other test findings.
What to Expect Afterward
There’s no recovery period. You can eat, drive, and return to normal activities immediately. The tracer leaves your body naturally over the following 24 to 48 hours, primarily through bile and urine. Drinking extra fluids can help clear it faster. The radiation dose is low, comparable to many standard diagnostic imaging tests.
If you’re breastfeeding, ask your doctor about whether to temporarily pump and discard milk for a short window after the scan. Pregnant women generally should not have this test unless the clinical need clearly outweighs the small radiation exposure to the fetus.
HIDA Scan vs. Other Imaging
Ultrasound is typically the first test ordered for gallbladder symptoms because it’s fast, inexpensive, and radiation-free. It excels at identifying gallstones and gallbladder wall thickening. But ultrasound shows anatomy, not function. It can’t tell you whether bile is actually flowing normally or whether the gallbladder is contracting as it should.
The HIDA scan fills that gap. It’s a functional test, revealing how the biliary system is working in real time rather than what it looks like in a snapshot. CT scans and MRI of the bile ducts (called MRCP) can also visualize the biliary anatomy in detail, but neither measures gallbladder contraction or tracks bile flow the way a hepatobiliary scan does. That’s why a HIDA scan is often ordered after an ultrasound comes back normal but symptoms persist.