The Hepatobiliary Iminodiacetic Acid (HIDA) scan, also known as cholescintigraphy, is a nuclear medicine imaging test used to visualize the liver, bile ducts, gallbladder, and small intestine. This procedure tracks the flow of bile, the digestive fluid produced by the liver, as it moves through the biliary system. When performed with cholecystokinin (CCK), the test’s primary function shifts from simply visualizing the pathway to actively assessing the gallbladder’s motor function. This combined approach is ordered by physicians to determine how effectively the gallbladder contracts and empties bile, which is often the cause of chronic upper abdominal pain.
Understanding the Components of the Test
The HIDA scan relies on an injected radioactive tracer, a radiopharmaceutical, which is processed by the body similarly to bilirubin. Once injected into a vein, the tracer is quickly taken up by the liver cells and excreted into the bile ducts. A gamma camera detects the rays emitted by the tracer to create a series of images that track its movement through the biliary tree and into the small intestine.
The tracer highlights the anatomy and patency of the bile ducts, showing if there is a blockage, such as from gallstones. If the gallbladder fills with the tracer, it indicates an open cystic duct, the small tube connecting the gallbladder to the main bile duct. The second component of this specific test is the administration of CCK, or its synthetic version called sincalide.
Cholecystokinin is a naturally occurring hormone that the body releases after eating a fatty meal to signal the gallbladder to contract. In the context of the HIDA scan, a measured dose of sincalide is administered intravenously to stimulate this contraction in a controlled manner. This chemical stimulation allows the medical team to quantify the organ’s ability to squeeze and empty its contents, combining anatomical visualization with a functional assessment of the gallbladder’s muscle strength.
Preparing for and Undergoing the Scan
Proper preparation is necessary to ensure the test yields accurate results. Patients are required to fast for at least four hours before the procedure, sometimes up to six hours. This fasting is important because eating causes the body to naturally release CCK, which would partially empty the gallbladder before the test begins, leading to inaccurate measurements.
Patients must also temporarily stop taking certain medications that can affect gallbladder function, most notably opioid pain relievers, for several hours before the procedure. These medications interfere with the natural muscle contractions of the gallbladder and can lead to a false result. The technician will first place an intravenous (IV) line for the injection of the radioactive tracer.
Once the initial tracer is injected, the patient lies still on a table while the gamma camera begins taking images. This first stage ensures the tracer moves properly from the liver and fills the gallbladder, which usually takes about an hour. After the gallbladder is clearly visualized, the cholecystokinin (sincalide) is slowly infused through the IV line over a period that typically lasts 30 to 60 minutes.
During the CCK infusion, the technician continues to take images to monitor the gallbladder’s contraction. Some patients may experience mild cramping, nausea, or abdominal discomfort that mimics their original symptoms. This sensation is expected, as it is a direct result of the gallbladder muscle forcefully squeezing in response to the hormone. The entire HIDA scan with CCK generally takes between 90 minutes and two hours to complete.
Interpreting the Gallbladder Ejection Fraction
The primary diagnostic metric derived from the HIDA scan with CCK is the Gallbladder Ejection Fraction (EF). The EF is a quantitative measurement that represents the percentage of bile the gallbladder empties in response to the CCK stimulation. This calculation is a direct measure of the organ’s motor function.
The EF is calculated by comparing the amount of radioactive tracer present in the gallbladder immediately before the CCK infusion to the amount remaining after the infusion is complete. A nuclear medicine physician uses computer software to analyze the images and determine this percentage. The resulting number is used to diagnose functional gallbladder disorders, even when no gallstones are present on other imaging tests.
A normal gallbladder ejection fraction is widely accepted as 38% or higher, particularly when the CCK is infused over 60 minutes. An abnormally low EF, typically defined as less than 35%, suggests that the gallbladder is not contracting effectively. This poor contractility is often a sign of chronic cholecystitis, which is long-term inflammation of the gallbladder, or biliary dyskinesia, a functional disorder of the organ’s movement.
Next Steps After Receiving Results
The interpretation of the Gallbladder Ejection Fraction guides the next steps in a patient’s treatment plan. If the HIDA scan with CCK reveals a normal EF, the physician will conclude that the gallbladder is functioning properly and is unlikely to be the cause of the patient’s abdominal pain. In this scenario, the medical team will explore other potential causes for the symptoms, such as irritable bowel syndrome, peptic ulcers, or acid reflux disease.
A finding of a low EF (less than 35%) is suggestive of a non-stone-related gallbladder issue, such as chronic cholecystitis or biliary dyskinesia. For patients who have experienced classic biliary pain alongside this abnormal result, the most common treatment path is a consultation with a surgeon. The definitive treatment for a dysfunctional gallbladder is a cholecystectomy, the surgical removal of the organ.
Clinical data suggests that patients with biliary pain and a confirmed low EF experience significant relief from their symptoms following gallbladder removal. The ordering physician will integrate the HIDA scan results with the patient’s clinical history and symptoms to determine the most appropriate course of action.