What is a Positive HIDA Scan Result?
A positive HIDA scan result indicates non-visualization of the gallbladder due to cystic duct obstruction, which is diagnostic of acute cholecystitis. 1, 2
Primary Interpretation: Acute Cholecystitis
- Non-filling of the gallbladder after radiotracer administration is the hallmark finding that defines a positive HIDA scan for acute cholecystitis 2
- The radiotracer (technetium-99m labeled hepatobiliary iminodiacetic acid) is extracted by hepatocytes and normally clears through the biliary system, filling the gallbladder within 30-60 minutes 2
- When the cystic duct is obstructed (typically by a gallstone), the radiotracer cannot enter the gallbladder, resulting in visualization of the liver and bile ducts but absence of gallbladder filling 2
Diagnostic Performance
HIDA scan has the highest sensitivity and specificity for acute cholecystitis compared to all other imaging modalities, with sensitivity of 84.2-89.3% versus 67.3% for ultrasound and 59.8% for CT (p=0.017) 1, 3
- Specificity ranges from 66.8-79% 1
- This superior diagnostic accuracy makes HIDA the gold standard when other imaging is equivocal 1
Alternative Interpretation: Chronic Acalculous Cholecystitis/Biliary Dyskinesia
A positive HIDA scan can also refer to gallbladder ejection fraction (GBEF) <35% after cholecystokinin (CCK) stimulation, which suggests chronic acalculous gallbladder disease or biliary dyskinesia 3, 4, 5, 2
- This interpretation applies specifically to patients with chronic biliary-type pain without gallstones, not acute cholecystitis 3, 4
- CCK-augmented HIDA scanning is NOT indicated for acute calculous cholecystitis where cystic duct obstruction is already present 3
- Patients with GBEF <35% who undergo cholecystectomy have 15-fold greater odds of symptom improvement compared to medical management 5
Important Caveat About Ejection Fraction
Symptom reproduction during CCK infusion may be more clinically significant than the ejection fraction itself 4
- In one study, all 42 patients (including 25 with normal GBEF >35%) who had symptom reproduction during CCK-HIDA and underwent cholecystectomy had resolution of symptoms at mean 18.7-month follow-up 4
- Only 2.4% experienced symptom recurrence, suggesting that normal GBEF does not rule out biliary etiology when symptoms are reproduced 4
Clinical Context and Limitations
HIDA scan utilization in clinical practice is limited due to required resources, time, and need for patient fasting 1, 3
- The test typically requires several hours to complete 3
- Patients must fast for several hours beforehand 3
- False-positive results can occur, and ERCP should be performed before surgical intervention if clinical suspicion is low 6
When HIDA is Indicated
HIDA scan should be considered when ultrasound findings are equivocal but clinical suspicion for acute cholecystitis remains high 3
- Ultrasound remains the initial imaging modality of choice due to lower cost, portability, and lack of radiation 3
- HIDA is reserved for selected patients depending on local expertise and availability 1
- In the era of Tokyo Guidelines 2018, HIDA may be overutilized, as clinical criteria alone can establish diagnosis in many cases 7