What does a positive or negative HIDA (Hepatobiliary Iminodiacetic Acid) scan indicate?

Understanding HIDA Scan: Interpretation and Clinical Significance

A HIDA (Hepatobiliary Iminodiacetic Acid) scan is the most sensitive and specific imaging modality for diagnosing acute cholecystitis, with sensitivity of 84.2-89.3% and specificity of 66.8-79%, significantly outperforming ultrasound and CT scans in diagnostic accuracy. 1, 2

What is a HIDA Scan?

• HIDA uses radioactive tracers that are extracted by hepatocytes and cleared through the biliary system similar to bilirubin 3
• The scan assesses gallbladder function by evaluating the ability of bile to flow from the liver through the biliary system into the gallbladder and small intestine 2

Positive vs. Negative HIDA Scan Results

Positive HIDA Scan (Non-Visualization of Gallbladder)

• Indicates cystic duct obstruction, typically due to gallstones or inflammation 2
• Diagnostic of acute cholecystitis when the radiotracer fills the biliary tree but fails to fill the gallbladder within 60 minutes 2, 3
• Sensitivity of 86.7-89.3% for detecting acute cholecystitis 1

Negative HIDA Scan (Normal Visualization)

• Shows normal filling of the gallbladder within the expected timeframe 3
• Effectively rules out acute cholecystitis due to high sensitivity 2, 4
• Does not exclude other gallbladder pathologies such as chronic cholecystitis or biliary dyskinesia 5

Clinical Significance and Interpretation

When to Consider a HIDA Scan

• When ultrasound findings are equivocal but clinical suspicion for acute cholecystitis remains high 2
• For patients with suspected acute cholecystitis but normal ultrasound findings 1, 2
• When other diagnostic possibilities for right upper quadrant pain have been ruled out 2

Limitations and Considerations

• Limited availability and time-consuming procedure compared to ultrasound 1
• False positive results may occur in patients with liver dysfunction or abnormal liver function tests 4, 6
• Patients should fast for several hours before undergoing a HIDA scan for optimal results 2

Special Applications

• CCK-augmented HIDA scanning is primarily used for diagnosing functional gallbladder disorder (biliary dyskinesia) and chronic acalculous cholecystitis, not for acute calculous cholecystitis 2, 5
• HIDA can also detect biliary obstruction, biliary leaks post-cholecystectomy, and hepatic transplantation complications 3

Diagnostic Algorithm

1. Begin with ultrasound as first-line imaging for suspected gallstone disease 2
2. If ultrasound confirms gallstones and signs of cholecystitis, no further imaging is needed 2
3. If ultrasound is equivocal but clinical suspicion remains high, proceed to HIDA scan 1, 2
4. A positive HIDA scan (non-visualization of gallbladder) confirms acute cholecystitis 2, 3
5. A negative HIDA scan effectively rules out acute cholecystitis but may warrant further investigation for other causes of symptoms 4, 5

Pitfalls to Avoid

• Relying solely on HIDA scan without initial ultrasound evaluation 2
• Misinterpreting HIDA results in patients with liver dysfunction 4
• Overlooking the possibility of false positive results in patients with abnormal liver function tests 6
• Using CCK-augmented HIDA for suspected acute calculous cholecystitis rather than its appropriate application in functional disorders 2, 5