HIDA Scan Explained: What to Expect During a Gallbladder Scan

• A HIDA scan (hepatobiliary scintigraphy) is a nuclear medicine test that evaluates gallbladder function and bile flow
• It uses a small amount of radioactive tracer to visualize the liver, gallbladder, bile ducts, and small intestine
• The test is primarily used to diagnose gallbladder disease, especially when ultrasound results are inconclusive
• The procedure takes 1 to 4 hours and is performed as an outpatient
• HIDA scans provide functional information that other imaging tests cannot, making them uniquely valuable for gallbladder evaluation

A HIDA scan, formally known as hepatobiliary iminodiacetic acid scintigraphy or cholescintigraphy, is a nuclear medicine imaging test used to evaluate the function of the liver, gallbladder, bile ducts, and small intestine. Unlike CT or ultrasound, which provide structural images (pictures of what things look like), a HIDA scan provides functional information (pictures of how things are working).

The test uses a radioactive tracer called a radiopharmaceutical. This tracer is injected into your bloodstream and is specifically taken up by the liver, excreted into bile, and then follows the normal path of bile flow through the bile ducts into the gallbladder and eventually into the small intestine. A special camera called a gamma camera detects the radioactive tracer and creates images that show the flow of bile in real time.

What "HIDA" stands for: Hepatobiliary IminoDiacetic Acid. HIDA refers to the type of radiopharmaceutical tracer used in the original version of the scan. Modern versions use similar but improved tracers, but the name "HIDA scan" has stuck.

How It Works

1. A radioactive tracer is injected into a vein in your arm
2. Your liver takes up the tracer from the bloodstream
3. The liver excretes the tracer into bile
4. Bile (with tracer) flows through the bile ducts to the gallbladder
5. The gallbladder stores and concentrates the bile
6. When stimulated, the gallbladder contracts and releases bile into the small intestine
7. The gamma camera tracks this entire process in real time

The tracer used contains a very small amount of radiation, comparable to the radiation from a standard X-ray. It is eliminated from your body within 24 to 48 hours.

Your doctor may order a HIDA scan for several reasons:

Primary Indications

Suspected gallbladder disease (cholecystitis): The most common reason for a HIDA scan is to evaluate suspected inflammation or infection of the gallbladder, particularly acute cholecystitis. The scan can detect blockage of the cystic duct, which is the hallmark of acute cholecystitis.

Biliary dyskinesia: This is a condition where the gallbladder does not contract properly, causing symptoms similar to gallstones (pain, nausea, bloating) even though no stones are present. The HIDA scan measures the gallbladder ejection fraction, which quantifies how well the gallbladder empties.

Bile leak: After gallbladder surgery or other abdominal procedures, bile can leak from the bile ducts into the abdominal cavity. A HIDA scan can detect this leak.

Biliary obstruction: Blockage of the bile ducts can be caused by gallstones, tumors, or strictures. A HIDA scan can identify the location and extent of the blockage.

Evaluation of biliary atresia: In newborns with jaundice, a HIDA scan can help diagnose biliary atresia, a condition where the bile ducts are abnormally formed.

When HIDA Scan Is Preferred Over Other Tests

• Ultrasound is inconclusive: If an ultrasound shows no gallstones but symptoms persist, a HIDA scan can evaluate gallbladder function
• Acalculous cholecystitis: Gallbladder inflammation without stones is best diagnosed with HIDA scan
• Post-surgical complications: Evaluating bile leaks or obstructions after gallbladder surgery
• Functional assessment needed: When your doctor needs to know how well the gallbladder is working, not just what it looks like

Proper preparation is important for accurate results.

Fasting Requirements

• Do not eat or drink for 4 to 6 hours before the scan
• This ensures your gallbladder is full and not actively contracting from a recent meal
• A full gallbladder provides the best images and most accurate ejection fraction measurement

Medication Considerations

• Tell your doctor about all medications you are taking, including over-the-counter drugs and supplements
• Opioid pain medications should be avoided for 6 to 12 hours before the scan because they can cause the sphincter of Oddi (the valve controlling bile flow) to spasm, which can interfere with results
• Medications that affect gallbladder function may need to be temporarily stopped
• Do not stop any medication without your doctor's instruction

Other Preparations

• Inform your doctor if you are pregnant, might be pregnant, or are breastfeeding
• Tell your doctor about any allergies, especially to medications or contrast materials
• If you have had a recent barium study or CT scan with contrast, let the facility know, as this can interfere with the HIDA scan
• Wear comfortable clothing without metal fasteners
• Plan to be at the facility for 2 to 4 hours

Step 1: Check-In and Preparation (15 minutes)

You will check in at the nuclear medicine department. A technologist will explain the procedure, answer questions, and verify your identity and the reason for the scan. You will be asked to remove metal objects from the area being scanned.

Step 2: IV Line Placement (5 minutes)

A small IV catheter will be placed in your arm or hand. The radioactive tracer will be injected through this line. You may feel a brief pinch when the IV is placed.

Step 3: Tracer Injection (1 minute)

The radioactive tracer is injected through the IV. The injection itself feels like any other IV injection. There are typically no immediate sensations from the tracer.

Step 4: Imaging Begins (60 to 90 minutes for standard scan)

You will lie flat on your back on an imaging table. The gamma camera will be positioned over your abdomen. The camera does not emit radiation; it only detects the radiation from the tracer already in your body.

• Images are taken continuously or at regular intervals
• You must lie very still during image acquisition
• The technologist may reposition the camera during the study
• You can breathe normally but should not talk or move during image capture

Step 5: Cholecystokinin (CCK) Injection (for ejection fraction measurement)

If your doctor ordered a gallbladder ejection fraction measurement (the most common type of HIDA scan for outpatient evaluation), you will receive an injection of cholecystokinin (CCK) or a synthetic version called sinalide. This hormone causes the gallbladder to contract.

• The CCK is injected slowly over 3 to 5 minutes through your IV
• You may experience mild nausea, abdominal cramping, or a warm sensation
• These sensations are temporary and normal; they mean the medication is working
• Additional images are taken for 30 to 60 minutes after the CCK injection to measure how much bile the gallbladder releases

Step 6: Completion

After all images are acquired, the IV will be removed and you can go home. You can eat, drink, and resume normal activities immediately.

Total time: Plan for 1.5 to 4 hours, depending on the specific protocol your doctor ordered.

A nuclear medicine physician or radiologist will interpret your HIDA scan and send a report to your doctor.

Key Measurements

Gallbladder ejection fraction (GBEF): This is the most important number on your HIDA scan report. It measures the percentage of bile your gallbladder expels when stimulated by CCK.

What Different Results Mean

Normal HIDA scan: The tracer flows normally from the liver through the bile ducts into the gallbladder and then into the small intestine. The gallbladder fills and empties normally. This effectively rules out gallbladder disease as the cause of your symptoms.

Non-visualization of the gallbladder: If the tracer reaches the liver and bile ducts but does not enter the gallbladder within 60 minutes, this suggests a blocked cystic duct. This is highly suggestive of acute cholecystitis (gallbladder inflammation), especially if you have symptoms.

Low ejection fraction: If the gallbladder fills normally but empties less than 35% after CCK stimulation, this suggests biliary dyskinesia. This condition can cause symptoms similar to gallstones (right upper quadrant pain, nausea, bloating) and may require gallbladder removal.

Bile leak: If tracer is seen outside the normal biliary pathways (in the abdominal cavity), this indicates a bile leak, which can occur after surgery.

Delayed biliary-to-bowel transit: If the tracer takes longer than expected to reach the small intestine, this may suggest a partial bile duct obstruction or sphincter of Oddi dysfunction.

Reproducing Symptoms During CCK Injection

An important aspect of the HIDA scan is whether the CCK injection reproduces your typical symptoms. If you experience your usual right upper quadrant pain during the CCK injection (even with a normal ejection fraction), some surgeons consider this a positive finding that supports gallbladder disease.

Radiation Exposure

The amount of radiation from a HIDA scan is small, comparable to a standard X-ray or a few weeks of natural background radiation. The tracer is eliminated from your body through urine and feces within 24 to 48 hours.

Radiation facts:

• The typical radiation dose is about 3 to 5 mSv (millisieverts)
• For comparison, a chest CT is about 7 mSv, and natural background radiation is about 3 mSv per year
• The benefits of an accurate diagnosis far outweigh the small radiation risk

Allergic Reactions

Allergic reactions to the radioactive tracer are extremely rare but can occur. Tell your doctor about any allergies before the scan.

CCK (Cholecystokinin) Side Effects

Side effects from the CCK injection are common but mild and temporary:

• Nausea (most common)
• Abdominal cramping
• Warm flushing sensation
• Dizziness

These effects typically resolve within minutes after the injection is complete.

Pregnancy and Breastfeeding

• Pregnancy: HIDA scans are generally avoided during pregnancy due to radiation exposure to the fetus. If absolutely necessary, the dose can be adjusted.
• Breastfeeding: The tracer can pass into breast milk. You may need to pump and discard breast milk for 24 to 48 hours after the scan. Discuss this with your doctor.

The cost varies based on your location, the facility, and whether additional measurements (like ejection fraction) are performed. Most insurance plans cover HIDA scans when ordered for appropriate medical indications.

Does a HIDA scan hurt? The scan itself is painless. You may feel a brief pinch when the IV is placed. The CCK injection can cause temporary nausea or cramping, but this is generally mild and passes quickly.

How is a HIDA scan different from a gallbladder ultrasound? Ultrasound provides structural images showing the size and shape of the gallbladder and whether stones are present. A HIDA scan provides functional information showing how well the gallbladder fills and empties. Your doctor may order both tests for a complete evaluation.

What happens if my HIDA scan is abnormal? Your doctor will discuss the results with you and recommend treatment. For a low ejection fraction (biliary dyskinesia), the most common treatment is surgical removal of the gallbladder (cholecystectomy). For acute cholecystitis, urgent treatment with antibiotics and surgery is typically needed.

Can I eat after my HIDA scan? Yes. You can resume normal eating and drinking immediately after the scan. The small amount of radioactive tracer will be eliminated through your urine and feces over the next 24 to 48 hours.

Why does the scan take so long? The HIDA scan tracks the flow of bile in real time, which is a gradual process. The tracer must be absorbed by the liver, excreted into bile, and then flow through the entire biliary system. This natural process takes time, and the imaging must capture each step.

Can I drive myself home after a HIDA scan? Yes. The procedure does not involve sedation, so you can drive yourself home and resume all normal activities immediately.

What if I am allergic to the tracer? True allergies to the radioactive tracer are extremely rare. If you have had a reaction to nuclear medicine tracers in the past, inform your doctor. Alternative imaging tests may be available.

A HIDA scan is a valuable diagnostic tool that provides unique functional information about your gallbladder and biliary system. While it takes longer than some other imaging tests, it offers insights that ultrasound and CT scans cannot provide, particularly when evaluating how well your gallbladder is working.

If your doctor has recommended a HIDA scan, understanding what to expect can help reduce anxiety and ensure the best possible results. Follow preparation instructions carefully, communicate with the imaging team, and use WellAlly to track your results and share them with your healthcare providers.