What is a HIDA (Hepatobiliary Iminodiacetic Acid) scan?

What is a HIDA Scan?

A HIDA (Hepatobiliary Iminodiacetic Acid) scan is a nuclear medicine imaging study that uses a radioactive tracer (Technetium-99m labeled iminodiacetic acid derivative) to evaluate the function and patency of the hepatobiliary system, including the liver, bile ducts, gallbladder, and cystic duct. 1

How the HIDA Scan Works

The radiotracer is administered intravenously and follows the same physiologic pathway as bilirubin:

• Hepatocyte uptake: The tracer is rapidly extracted by liver cells within 5 minutes of injection 1
• Biliary excretion: Maximum liver uptake occurs at 11 minutes, followed by excretion into the bile ducts 1
• Gallbladder visualization: In normal patients, the hepatic duct and gallbladder are visualized by 10-15 minutes post-injection 1
• Intestinal transit: Radiotracer appears in the small intestine by 30-60 minutes in patients with normal hepatobiliary function 1, 2

The scan is performed continuously for approximately 1 hour using a gamma camera to track the tracer's movement through the biliary system 3.

Primary Clinical Indications

Acute Cholecystitis (Most Common Indication)

HIDA scan has the highest sensitivity (84.2-89.3%) and specificity (66.8-79%) for diagnosing acute cholecystitis compared to all other imaging modalities, significantly outperforming ultrasound (67.3% sensitivity) and CT (59.8% sensitivity) 4, 5, 6.

• Diagnostic criterion: Non-visualization of the gallbladder after 60 minutes indicates cystic duct obstruction, confirming acute cholecystitis 2, 7
• Negative predictive value: Visualization of the gallbladder effectively excludes acute cholecystitis 7

Chronic Acalculous Cholecystitis and Biliary Dyskinesia

CCK-augmented HIDA scanning is indicated for functional gallbladder disorders, not for acute calculous cholecystitis where obstruction is already present 5, 6:

• Technique: Cholecystokinin (CCK/sincalide) is infused at 0.02 μg/kg over 60 minutes to stimulate gallbladder contraction 5
• Abnormal result: Gallbladder ejection fraction (GBEF) <38% suggests chronic acalculous cholecystitis or biliary dyskinesia 5, 6
• Clinical utility: In one study, 82% of patients with abnormal GBEF who underwent cholecystectomy achieved complete symptom resolution 8

Other Indications

• Biliary obstruction: High-grade obstruction shows persistent hepatogram without biliary clearance before ductal dilatation is visible on other imaging 2
• Bile leak detection: Identifies post-cholecystectomy or post-transplant biliary leakage 2
• Congenital anomalies: Evaluates biliary tract anatomic variants 9

Patient Preparation Requirements

Fasting

Patients must fast for 4-6 hours (optimally overnight) to ensure adequate gallbladder filling with bile 5, 6. This is critical for accurate interpretation.

Medication Restrictions

Anticholinergic drugs must be withheld for at least 48 hours before scanning because they directly impair gallbladder contraction and cause false-positive results 5, 6.

Additional medications to avoid:

• Opiates: Withhold for at least 48 hours 5, 6
• Other drugs to avoid within 24 hours: Nifedipine, indomethacin, octreotide, theophylline, benzodiazepines, phentolamine, isoproterenol, progesterone 5
• Nicotine and alcohol: Should also be avoided 5

Clinical Algorithm for Use

When to Order HIDA Scan

The World Society of Emergency Surgery recommends HIDA scan as second-line imaging when ultrasound is equivocal but clinical suspicion for acute cholecystitis remains high 4, 5, 6:

1. First-line: Ultrasound for all patients with suspected acute cholecystitis 5, 6
2. If ultrasound confirms gallstones and cholecystitis: No further imaging needed 5
3. If ultrasound is equivocal: Consider HIDA scan (without CCK) to assess for cystic duct obstruction 5, 6
4. Alternative: CT scan may be used as next step in non-pregnant adults 6

When NOT to Order HIDA Scan

• Acute calculous cholecystitis with clear ultrasound findings: HIDA adds no value 5
• CCK-augmented HIDA is NOT indicated for acute calculous cholecystitis where cystic duct obstruction is already present 5, 6

Limitations and Practical Considerations

Clinical Practice Barriers

HIDA scan utilization is limited in clinical practice due to required resources, time (1+ hour procedure), and availability, which is why it remains positioned as second or third-line imaging 4, 6.

Effect of Jaundice

Elevated serum bilirubin increases renal excretion of the radiotracer and delays hepatobiliary transit:

• In patients with mean bilirubin of 9.8 mg/dL, urinary excretion increased from 1% to 3% in the first 3 hours 1
• Blood clearance is slower (twice as high at 10 minutes) 1
• Image quality frequently diminishes in jaundiced patients 1
• In total obstructive jaundice, the isotope may be excreted through the kidneys without liver visualization 3

False Results

Common pitfalls:

• False positive (non-visualization of gallbladder): Prolonged fasting >24 hours, recent meal, hepatocellular disease, medications listed above 5, 6
• False negative (gallbladder visualization): Partial cystic duct obstruction, chronic cholecystitis with patent cystic duct 7

Comparison to Other Imaging

• Ultrasound: Lower sensitivity (67-73%) but first-line due to cost, availability, portability, and lack of radiation 4, 5
• CT: Poor diagnostic accuracy (59.8% sensitivity) for acute cholecystitis 4
• MRI/MRCP: Comparable accuracy to ultrasound but more expensive and less available 4