What is the purpose and procedure of a HIDA (Hepatobiliary Iminodiacetic Acid) scan?

HIDA Scan: Purpose and Procedure

A HIDA (Hepatobiliary Iminodiacetic Acid) scan is the gold standard for diagnosing acute cholecystitis, with a sensitivity of 86.7-89.3% and specificity of 66.8-79%, and is also valuable for assessing gallbladder function, detecting biliary obstruction, and identifying bile leaks. 1

Purpose of HIDA Scan

HIDA scans are nuclear medicine imaging studies that evaluate the function of the hepatobiliary system based on physiology rather than just anatomy. The primary purposes include:

• Diagnosing acute cholecystitis (primary indication)
• Assessing gallbladder function through ejection fraction calculation
• Detecting biliary obstruction before ductal dilation occurs
• Identifying partial biliary obstruction due to stones, strictures, or sphincter dysfunction
• Confirming biliary leakage after cholecystectomy or liver transplantation
• Diagnosing chronic acalculous gallbladder disease 1, 2

HIDA Scan Procedure

Patient Preparation

• Fasting for at least 4-6 hours prior to the study (optimally overnight)
• Should be performed on an outpatient basis, not during acute hospitalization
• Withholding medications that affect gallbladder contraction:
  • Opiates and anticholinergics: 48 hours before testing
  • Other medications (nifedipine, indomethacin, octreotide, etc.): 24 hours before
  • Nicotine and alcohol should also be avoided 3

Standard Procedure Steps

1. An intravenous line is started with the patient lying supine on the imaging table
2. A radioactive tracer (Tc-99m HIDA) is injected intravenously
3. Images are acquired for up to 60 minutes to assess gallbladder visualization
4. If the gallbladder is not visualized by 60 minutes in a properly prepared patient, this indicates potential acute or chronic cholecystitis 3, 1

For Suspected Acute Cholecystitis

• Non-visualization of the gallbladder with visualization of the common bile duct is diagnostic of acute cholecystitis
• If the gallbladder is not visualized by 60 minutes, morphine (0.04 mg/kg) may be administered intravenously
• Imaging continues for an additional 30 minutes after morphine administration 1, 4

For Gallbladder Function Assessment (CCK-CS Protocol)

1. After gallbladder visualization, the camera is placed in left anterior oblique projection (35-40 degrees)
2. Sincalide (CCK) is administered at 0.02 μg/kg diluted in saline and infused continuously over 60 minutes
3. Dynamic imaging (1 image per minute) is performed during the infusion
4. Gallbladder ejection fraction (GBEF) is calculated, with <38% considered abnormal 3

Interpretation of Results

• Normal study: Visualization of the gallbladder within 60 minutes (excludes acute cholecystitis)
• Acute cholecystitis: Non-visualization of the gallbladder despite visualization of the common bile duct and intestine
• Biliary obstruction: Persistent hepatogram without biliary clearance
• Chronic acalculous gallbladder disease: Abnormal gallbladder ejection fraction (<38%) after sincalide infusion 3, 2, 4

Clinical Considerations and Caveats

• Contraindications: Known allergic reaction to sincalide and intestinal obstruction; pregnancy is a relative contraindication

• False positives can occur in:

  • Fasting for >24 hours
  • Severe liver disease
  • Total parenteral nutrition
  • Severe intercurrent illness
  • Chronic cholecystitis

• False negatives are rare but can occur in early/partial cystic duct obstruction 1, 5

• While ultrasound is typically the initial imaging modality for suspected gallbladder disease (sensitivity 81-88%, specificity 80-83%), HIDA scan is often the next step when ultrasound results are equivocal but clinical suspicion for acute cholecystitis remains high 1