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 of the liver, gallbladder, bile ducts, and cystic duct by tracking bile flow through the hepatobiliary system. 1, 2

How the Test Works

Mechanism of Action:

• The radiotracer is injected intravenously and rapidly extracted by hepatocytes in the liver, similar to how bilirubin is processed 1, 2
• In normal subjects, the tracer is cleared from blood circulation within 10 minutes (83% cleared), with only 17% remaining in the bloodstream 1
• The liver visualizes by 5 minutes, reaches maximum uptake at 11 minutes, and the hepatic duct and gallbladder appear by 10-15 minutes 1
• Intestinal activity is typically seen by 30-60 minutes in patients with normal hepatobiliary function 1
• Only 1% of the injected dose is excreted in urine during the first 3 hours in normal patients 1

Primary Clinical Indications

Acute Cholecystitis Diagnosis:

• 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 3, 4
• The diagnosis is made by demonstrating non-filling of the gallbladder due to cystic duct obstruction 2, 5
• HIDA sensitivity (84.2%) significantly exceeds ultrasound (67.3%) and CT (59.8%) for acute cholecystitis (p=0.017) 3
• An absent gallbladder image with a normal hepatogram strongly supports acute cholecystitis, while gallbladder visualization excludes this diagnosis 5

Functional Gallbladder Disorder (Biliary Dyskinesia):

• CCK-augmented HIDA scanning measures gallbladder ejection fraction (GBEF) to diagnose chronic acalculous cholecystitis and functional gallbladder disorder 4, 6
• The standardized protocol uses 0.02 μg/kg sincalide infused over 60 minutes, with abnormal GBEF defined as <38% 4, 6
• CCK-augmented HIDA is NOT indicated for acute calculous cholecystitis where cystic duct obstruction is already present 4

Other Diagnostic Applications:

• Detection of high-grade biliary obstruction before ductal dilatation occurs (shows persistent hepatogram without biliary clearance) 2
• Diagnosis of partial biliary obstruction from stones, strictures, or sphincter of Oddi dysfunction 2
• Confirmation of biliary leakage post-cholecystectomy or after hepatic transplantation 2
• Evaluation of congenital gallbladder and biliary duct anomalies 7

Patient Preparation Requirements

Critical Pre-Test Restrictions:

• Patients must fast for 4-6 hours (optimally overnight) to ensure adequate gallbladder filling with bile 4, 6
• Anticholinergic drugs must be withheld for at least 48 hours because they impair gallbladder contraction and cause false-positive results 4, 6
• Opiates must be withheld for at least 48 hours before testing 4, 6
• Other medications to avoid within 24 hours include nifedipine, indomethacin, octreotide, theophylline, benzodiazepines, phentolamine, isoproterenol, and progesterone 4
• Nicotine and alcohol should also be avoided prior to testing 4

Clinical Positioning in Diagnostic Algorithm

When to Order HIDA:

• Ultrasound remains the first-line imaging modality for suspected gallstone cholecystitis due to lower cost, portability, and lack of radiation 4, 6
• Consider HIDA scan when ultrasound findings are equivocal but clinical suspicion for acute cholecystitis remains high 4, 6
• HIDA is recommended after other diagnostic possibilities for right upper quadrant pain have been ruled out 4

Practical Limitations:

• HIDA scan utilization in clinical practice is limited due to required resources, time, and availability 3, 6
• This resource intensity explains why HIDA is positioned as second or third-line imaging after ultrasound and potentially CT 6

Special Considerations in Jaundiced Patients

Impact of Elevated Bilirubin:

• Elevated serum bilirubin levels increase renal excretion of the radiotracer 1
• In patients with mean bilirubin of 9.8 mg/dL, urinary excretion increases to 3% in the first 3 hours and 14.9% during 3-24 hours (compared to 1% in normal patients) 1
• Blood retention at 10 minutes may be twice as high or more in jaundiced patients 1
• Hepatobiliary transit is delayed, visualization times increase, and image quality frequently diminishes 1

Common Pitfalls to Avoid

• Do not use rapid CCK infusion (<30 minutes), as this causes non-specific abdominal symptoms that confound interpretation 6
• Failure to withhold anticholinergics or opiates will result in spuriously decreased GBEF and false-positive results 4, 6
• The test should be performed on an outpatient basis when possible, not during acute illness, particularly for functional gallbladder assessment 4
• In chronic gallbladder disease without acute inflammation, HIDA offers no advantage over oral cholecystogram 5