The gallbladder is a small organ located beneath the liver that plays a role in the digestive system. Its primary job is to store and concentrate the greenish-yellow fluid (bile) that the liver continuously generates. When fatty food enters the small intestine, the gallbladder receives a signal to contract and squeeze the stored bile into the digestive tract to help break down fats.
When patients experience symptoms like abdominal pain, nausea, or vomiting, doctors use imaging like ultrasound to check for structural problems, such as gallstones or inflammation. However, sometimes the gallbladder looks healthy on standard scans but is failing to contract and empty bile effectively. When a structural issue is not apparent, a specialized test is necessary to assess the organ’s functional capacity, moving the diagnosis beyond simple anatomy.
Identifying the Gallbladder Function Test
The primary tool for assessing the mechanical function of this organ is the Hepatobiliary Iminodiacetic Acid scan, commonly abbreviated as a HIDA scan. This procedure is also known as cholescintigraphy or hepatobiliary scintigraphy, and it uses principles of nuclear medicine to track the movement of bile. Unlike an ultrasound or CT scan, which provides a static picture of the organ’s structure, the HIDA scan is a dynamic test that monitors a physiological process.
The test is specifically designed to diagnose functional disorders of the biliary system, most notably chronic cholecystitis or biliary dyskinesia. Biliary dyskinesia is a motility disorder where the gallbladder has difficulty squeezing out its contents, leading to symptoms even though no gallstones or blockages are present. By tracking a radioactive tracer as it moves through the liver, gallbladder, and bile ducts, the scan provides visual evidence of whether the organ is functioning properly or failing to contract.
How the Procedure is Performed
The HIDA scan procedure begins with the placement of an intravenous (IV) line, typically in the patient’s arm or hand. A small dose of a radioactive tracer is then injected into the bloodstream through this IV. This tracer is designed to mimic natural bile, meaning the liver cells rapidly absorb it from the blood and excrete it into the bile ducts.
A specialized device called a gamma camera is positioned over the patient’s abdomen to continuously capture images as the tracer moves. The camera tracks the radiotracer’s path, first observing it in the liver, then documenting its entry and concentration within the gallbladder. This initial imaging confirms that the tracer is successfully reaching the organ under investigation.
The next phase involves stimulating the gallbladder to contract. A synthetic hormone, often Cholecystokinin (CCK) or a similar fatty acid stimulant like sincalide, is administered slowly through the IV. CCK is the body’s natural messenger, released after eating, that tells the gallbladder to empty, and the injection mimics this digestive response.
The stimulant is typically infused over about 60 minutes while the gamma camera continues to record the process. This continuous imaging allows technicians to measure precisely how much bile the gallbladder expels in response to the hormonal trigger. During the CCK infusion, some patients may experience a reproduction of their typical abdominal symptoms, which further supports the diagnosis of a functional gallbladder problem.
Interpreting the Ejection Fraction Results
The most important result derived from the HIDA scan is the Gallbladder Ejection Fraction (EF). The EF is a quantitative metric, expressed as a percentage, that represents the total amount of bile the gallbladder successfully ejected following the CCK stimulation. It is calculated by comparing the amount of radioactive tracer present in the gallbladder before and after the contraction stimulus.
This percentage directly indicates the efficiency of the organ’s muscle contraction. A normal EF value is generally considered to be 38% or greater, though some centers may use a slightly different threshold. Values falling below this range are considered abnormal and suggest a functional failure, or hypokinesia, of the gallbladder.
An EF significantly below the normal threshold, such as less than 35%, is often the diagnostic confirmation of biliary dyskinesia. This indicates that the organ is failing to empty adequately, which is likely the source of the patient’s pain and digestive issues. Conversely, an EF that is very high, sometimes exceeding 80%, may indicate a condition called biliary hyperkinesia, which can also be associated with symptoms.
Patient Preparation and Post-Test Advice
Preparation for the HIDA scan is strict, as certain conditions can artificially alter the results. Patients must fast (not eat or drink anything other than water) for about four hours before the procedure. This fasting ensures the gallbladder is full of bile and ready to be stimulated, providing a baseline measurement.
Patients must inform the healthcare team about all current medications, as some drugs can interfere with the contraction response. Opioid or morphine-based pain medications should be avoided for about 24 hours prior to the scan, as they can cause the sphincter controlling bile flow to constrict and skew results. If a patient is pregnant or breastfeeding, they must inform their physician, as the radioactive tracer may pose a risk.
Following the procedure, which typically takes one to two hours, patients can usually return to their normal daily activities immediately. The radioactive tracer used in the test is generally safe and only exposes the patient to a very small amount of radiation. To help the small amount of tracer pass quickly out of the body, patients are often advised to drink extra water for the remainder of the day.