A HIDA (Hepatobiliary Iminodiacetic Acid) scan is a diagnostic imaging procedure that evaluates the function of the liver, gallbladder, and bile ducts. It helps medical professionals understand how bile is produced, flows, and is stored. This test is frequently used to diagnose conditions affecting the biliary system, such as inflammation or blockages.
Preparing for Your HIDA Scan
Preparing for a HIDA scan involves specific instructions to ensure accurate results. You will generally be asked to fast for 4-12 hours. While fasting, you may usually drink water, but confirm this with your healthcare provider.
Discuss any medications you are currently taking with your doctor. Certain pain medications, particularly opioids or morphine, may need to be stopped at least 24 hours prior, as they can interfere with test results. Wear comfortable, loose-fitting clothing and remove any jewelry or metal objects, as these can interfere with imaging equipment. Bringing a list of your current medications is advisable.
The HIDA Scan Procedure
The HIDA scan begins with you lying on an examination table. A healthcare professional inserts an intravenous (IV) catheter, typically in your arm or hand. Through this IV, a small amount of radioactive tracer, commonly technetium-99m, is injected into your bloodstream. This tracer is absorbed by liver cells, similar to how they absorb bile.
Once injected, the tracer travels through your liver, then into the bile ducts, and subsequently fills the gallbladder. From the gallbladder, it normally passes into the small intestine. A gamma camera is positioned over your abdomen to detect the gamma rays emitted by the tracer. This camera captures images over time, typically for 60-90 minutes, to track the tracer’s movement. Remain as still as possible during imaging to ensure clear pictures.
Additional medications might be administered during the scan, depending on the reason for the test. If evaluating gallbladder function, cholecystokinin (CCK), also known as sincalide, may be given intravenously. This stimulates the gallbladder to contract and release bile, mimicking a natural digestive response. When CCK is administered, you might experience mild abdominal cramping or nausea, which is usually temporary.
If a bile duct obstruction is a concern, morphine might be given to help the tracer enter the gallbladder. Morphine causes the sphincter of Oddi to constrict, encouraging the tracer to back up and fill the gallbladder if it hasn’t visualized. The entire procedure usually lasts 1-4 hours, but sometimes longer if delayed imaging is necessary.
After Your HIDA Scan
Once the HIDA scan is complete, you can typically resume normal activities immediately. There is no sedation involved, so you should not need assistance to go home. To help your body eliminate the small amount of radioactive tracer, it is recommended to drink plenty of fluids for the next 24 hours. Most of the tracer will leave your body through urine and stool within a day or two.
While the amount of radiation is minimal, breastfeeding mothers should temporarily stop breastfeeding for 24-72 hours and discard any pumped milk to prevent tracer transfer to the infant. Your healthcare provider will inform you when and how your results will be communicated, usually within a few business days.
Interpreting HIDA Scan Results
A normal HIDA scan indicates that the radioactive tracer moved freely from your liver, filled your gallbladder, and then passed into your small intestine within the expected timeframe. This suggests that the bile ducts are open and the gallbladder is functioning correctly.
Abnormal results can point to various issues. If the tracer moves slowly, it might suggest an obstruction in the bile ducts or a problem with liver function. If the gallbladder does not visualize at all, it can indicate acute inflammation of the gallbladder (acute cholecystitis), often due to a blockage.
A low gallbladder ejection fraction, measured after CCK administration, suggests the gallbladder is not contracting effectively, which can be a sign of chronic inflammation or dysfunction. If the tracer is detected outside the normal biliary pathway, it could indicate a bile leak. Your doctor will interpret these findings with your symptoms and other diagnostic tests to determine a diagnosis.
Safety and Considerations
HIDA scans are generally considered safe, with very few associated risks. The amount of radiation exposure from the radioactive tracer is low, comparable to that received from a standard X-ray or typical background radiation over a year. The tracer is quickly eliminated from the body, further minimizing exposure.
While rare, some individuals may experience a mild allergic reaction to the radioactive tracer or the CCK medication. Bruising at the injection site is also a possibility. Inform your healthcare provider if you are pregnant or breastfeeding, as HIDA scans are typically avoided during pregnancy due to potential risks to the developing fetus. Your doctor will weigh the benefits and risks of the procedure in your specific situation.