What Is a HIDA Scan?
A HIDA scan (hepatobiliary iminodiacetic acid scan) is a nuclear medicine imaging test that tracks the flow of bile from the liver through the bile ducts, into the gallbladder, and out into the small intestine. It is sometimes called a hepatobiliary scan or cholescintigraphy.
Unlike an ultrasound or CT scan that shows the shape and structure of the gallbladder, a HIDA scan shows how the biliary system is functioning. It answers questions like: Is the gallbladder filling normally? Is bile draining properly? Is there an obstruction or leak somewhere in the system?
How the Scan Works
The test uses a radioactive tracer, typically Tc-99m mebrofenin or a similar HIDA agent, that is taken up by the liver cells and excreted into the bile in the same way the liver handles natural bile components. This allows the tracer to flow through the biliary system, acting as a marker that the gamma camera can follow in real time.
Here is the step-by-step process:
Injection: The tracer is injected into a vein in the arm. Within minutes, the liver begins extracting the tracer from the blood and processing it into bile.
Imaging: You lie on your back under a gamma camera that is positioned over your abdomen. The camera captures images continuously or at regular intervals over a period of 60 to 90 minutes. These images show the tracer moving from the liver into the bile ducts, filling the gallbladder, and eventually passing into the duodenum (the first part of the small intestine).
Delayed images: If the gallbladder does not fill within the standard imaging window, delayed images may be taken at 2, 3, or even 4 hours after injection. In some protocols, a small dose of morphine is given intravenously to contract the sphincter of Oddi (the valve at the end of the common bile duct), which encourages the gallbladder to fill if it is going to. This morphine-augmented protocol can shorten the total scan time compared to simply waiting for delayed images.
CCK stimulation (if needed): In some cases, particularly when gallbladder function rather than obstruction is the question, a hormone called cholecystokinin (CCK) is injected to stimulate the gallbladder to contract. The rate at which the gallbladder empties in response to CCK is measured as the gallbladder ejection fraction (GBEF).
What Conditions Does a HIDA Scan Diagnose?
Acute Cholecystitis
This is the most common reason for ordering a HIDA scan. Acute cholecystitis is inflammation of the gallbladder, usually caused by a gallstone blocking the cystic duct (the tube connecting the gallbladder to the common bile duct).
On a HIDA scan, acute cholecystitis shows a characteristic pattern: the tracer fills the liver and bile ducts normally and reaches the small intestine, but the gallbladder does not fill even after extended imaging or morphine augmentation. This non-visualisation of the gallbladder is the hallmark finding and has high diagnostic accuracy for acute cholecystitis.
Ultrasound is usually the first imaging test for suspected gallbladder disease, but when ultrasound results are equivocal or the clinical picture is unclear, the HIDA scan provides a definitive functional assessment.
Chronic Cholecystitis and Biliary Dyskinesia
Some patients have recurrent episodes of right upper abdominal pain after meals but no gallstones on ultrasound. In these cases, the question is whether the gallbladder is functioning normally.
A HIDA scan with CCK stimulation measures the gallbladder ejection fraction. A low ejection fraction (typically below 35-40%, though thresholds vary by institution) suggests the gallbladder is not contracting adequately, a condition called biliary dyskinesia. This finding, combined with the patient’s symptoms, may support a recommendation for cholecystectomy (gallbladder removal).
Biliary Obstruction
If a gallstone migrates out of the gallbladder and lodges in the common bile duct, it can block bile flow to the intestine. On a HIDA scan, this appears as tracer accumulating in the liver and bile ducts without reaching the duodenum. The pattern of obstruction can help distinguish between different levels of blockage.
Bile Leak
After gallbladder surgery or liver procedures, a bile leak can develop. The HIDA scan can detect bile leaking outside the normal biliary channels, appearing as tracer collecting in an abnormal location within the abdomen. This is a valuable diagnostic tool in the post-surgical setting when a bile leak is suspected clinically.
Neonatal Jaundice (Biliary Atresia vs Neonatal Hepatitis)
In newborns with persistent jaundice, a HIDA scan can help distinguish biliary atresia (a condition where bile ducts are absent or blocked, requiring urgent surgery) from neonatal hepatitis (which is managed medically). If the tracer reaches the intestine, biliary atresia is unlikely. If it does not, further evaluation for biliary atresia is warranted.
Preparation for a HIDA Scan
Preparation is straightforward but important for accurate results:
- Fasting: You will be asked to fast for 4 to 6 hours before the scan. This ensures the gallbladder has had time to fill with bile and is ready to be visualised. However, fasting for more than 24 hours can also interfere with the scan (the gallbladder becomes over-distended and may not take up more bile), so follow the specific timing your doctor or imaging centre provides.
- Medications: Inform the nuclear medicine team of all medications you are taking. Opioid pain medications can affect bile duct motility and may need to be paused before the scan. Your doctor will advise on any adjustments.
- Previous imaging: Bring any recent ultrasound or CT reports, as these provide context that helps the nuclear medicine physician interpret the HIDA scan findings.
What to Expect During the Scan
The scan itself is painless apart from the initial IV injection. You lie still on the imaging table while the camera captures images. Most patients describe it as uneventful, though the total time commitment can be significant if delayed images are needed.
- Standard scan: 60 to 90 minutes
- With morphine augmentation: approximately 90 minutes to 2 hours
- With delayed imaging: up to 4 hours in some cases
- With CCK stimulation for ejection fraction: add 30 to 45 minutes
If CCK is administered, some patients experience brief abdominal cramping or nausea, which typically resolves within a few minutes.
After the Scan
There are no restrictions after a HIDA scan. You can eat, drink, drive, and return to normal activities immediately. The radioactive tracer is excreted naturally and leaves the body within a day or two. The radiation dose is low and within standard medical imaging limits.
Results are typically reported within a day and sent to your referring doctor, who will discuss the findings and next steps with you. Whether the scan points toward surgery, medical management, or additional testing depends on the specific findings and your overall clinical picture.
If your doctor has recommended a HIDA scan, it means they need functional information about your biliary system that structural imaging alone cannot provide. The scan is safe, well-established, and gives clear answers to specific clinical questions about your gallbladder and bile ducts.