HIDA Scan: Purpose and Procedure
What is a HIDA Scan?
A HIDA (Hepatobiliary Iminodiacetic Acid) scan is a nuclear medicine imaging study that uses radioactive tracers extracted by hepatocytes and cleared through the biliary system, similar to bilirubin, to evaluate gallbladder and biliary tract function based on physiology rather than anatomy 1.
Primary Clinical Indications
Acute Cholecystitis
HIDA scan has the highest sensitivity and specificity for diagnosing acute cholecystitis compared to other imaging modalities, with sensitivity of 84.2-89.3% versus 67.3% for ultrasound and 59.8% for CT 2. The diagnosis is made by demonstrating non-filling of the gallbladder due to cystic duct obstruction 3, 1.
- In patients with suspected acute cholecystitis where ultrasound is equivocal but clinical suspicion remains high, HIDA scan should be considered as the next diagnostic step 2, 4
- The scan visualizes the gallbladder in all normal patients but in none with acute cholecystitis 3
- When the gallbladder is visualized on HIDA scan, acute cholecystitis is effectively excluded 3
Biliary Dyskinesia and Chronic Acalculous Cholecystitis
CCK-augmented HIDA scanning with calculation of gallbladder ejection fraction is the gold standard functional test for diagnosing biliary dyskinesia 5, 2.
- An ejection fraction <40% after cholecystokinin (sincalide) infusion indicates abnormal gallbladder function 6
- This test is primarily indicated for functional gallbladder disorder and chronic acalculous cholecystitis, NOT for acute calculous cholecystitis where cystic duct obstruction is already present 2
- Standardized protocols require 0.02 μg/kg sincalide infused over 60 minutes for reliable results 2
Other Diagnostic Applications
HIDA scanning aids in diagnosing:
- Partial biliary obstruction from stones, strictures, or sphincter of Oddi dysfunction 1, 4
- High-grade biliary obstruction before ductal dilatation occurs, showing persistent hepatogram without biliary clearance 1
- Biliary leakage post-cholecystectomy or after hepatic transplantation 1, 7
Diagnostic Algorithm
Step 1: Initial Imaging
Begin with abdominal ultrasound as first-line imaging for suspected biliary disease 2, 4.
Step 2: When Ultrasound is Diagnostic
If ultrasound confirms gallstones with signs of cholecystitis, no further imaging is needed 2.
Step 3: When Ultrasound is Equivocal
Consider HIDA scan without CCK to assess for cystic duct obstruction if ultrasound is equivocal for acute cholecystitis 2.
Step 4: For Biliary-Type Pain Without Gallstones
If ultrasound shows no cholelithiasis but biliary colic persists, employ CCK-HIDA scan early as the definitive functional test 5.
Step 5: Alternative Advanced Imaging
CT with IV contrast or MRI/MRCP may be obtained if initial imaging remains inconclusive 4.
Procedure Details
Patient Preparation
- Patients must fast for several hours before the scan 2
- This ensures adequate gallbladder filling for accurate assessment
Scan Protocol
- Radiotracer (99mTc-labeled HIDA analog) is injected intravenously 3, 1
- Dynamic imaging is performed during the first hour using a gamma camera 3
- Images and time-activity curves are generated to assess hepatic uptake, biliary excretion, and gallbladder filling 3
- For functional assessment, CCK is infused after initial imaging to stimulate gallbladder contraction 6
Important Limitations and Pitfalls
False Positives for Acute Cholecystitis
Non-visualization of the gallbladder can occur in:
- Hepatocellular disease (42% of cases show non-visualization due to poor uptake) 3
- Biliary obstruction (no visualization due to poor secretion) 3
- Prolonged fasting or critical illness
Practical Constraints
HIDA scan utilization in clinical practice is limited by required resources, specialized equipment, and time compared to ultrasound 4.
CCK-HIDA Limitations
Despite abnormal ejection fractions, outcomes after cholecystectomy for acalculous disease can be variable, with some studies showing excellent outcomes regardless of ejection fraction results 8.
Clinical Outcomes
For patients with typical biliary pain, normal ultrasound, and abnormal HIDA scan (<40% ejection fraction):