What is the protocol for a Hepatobiliary Iminodiacetic Acid (HIDA) scan, including preparation, procedure, and precautions, especially for patients with impaired liver or kidney function?

HIDA Scan Protocol

Radiopharmaceutical and Administration

The standard HIDA scan uses Tc-99m mebrofenin at 5 mCi (185 MBq) administered intravenously, which is the preferred agent over other HIDA derivatives due to superior hepatic uptake and biliary excretion even in patients with elevated bilirubin. 1, 2

• Tc-99m disofenin is an acceptable alternative if mebrofenin is unavailable 1
• The radiopharmaceutical is rapidly cleared from circulation with only 17% remaining in blood at 10 minutes in normal subjects 2
• Liver visualization occurs by 5 minutes, with maximum hepatic uptake at 11 minutes post-injection 2

Patient Preparation

Patients must fast for a minimum of 4-6 hours, though overnight fasting is optimal, to ensure adequate gallbladder filling and avoid false-positive results. 3

Critical Medication Restrictions:

• Opiates and anticholinergics must be withheld for at least 48 hours before testing 3
• The following medications should be avoided for 24 hours prior: nifedipine, indomethacin, octreotide, theophylline, benzodiazepines, phentolamine, isoproterenol, and progesterone 3
• Nicotine and alcohol should also be avoided before testing 3

Testing Conditions:

• CCK-cholescintigraphy should be performed on an outpatient basis only, not during acute illness or hospitalization, as confounding factors in acutely ill patients can spuriously decrease gallbladder ejection fraction 3

Standard Imaging Protocol for Acute Cholecystitis

Dynamic imaging is performed continuously for up to 60 minutes after radiotracer injection to assess gallbladder filling. 3

• A large field-of-view gamma camera with low-energy collimator is used 3
• Images are acquired with 140 keV photopeak and 20% window 3
• If the gallbladder has not filled by 60 minutes in a properly prepared patient, this is reported as abnormal and consistent with either acute or chronic cholecystitis depending on clinical presentation 3

Morphine-Augmented Protocol Option:

• For suspected acute cholecystitis, 2 mg morphine IV push can be administered at bedside before imaging, which increases specificity to 95% and positive predictive value to 81% compared to 83% and 45% respectively with delayed imaging alone 4
• This modified protocol eliminates the need for delayed imaging up to 4 hours and improves accuracy from 84% to 95% 4

CCK-Cholescintigraphy Protocol for Functional Gallbladder Disorder

Sincalide (synthetic CCK) at 0.02 μg/kg is infused intravenously over 60 minutes AFTER gallbladder filling is confirmed to calculate gallbladder ejection fraction (GBEF). 3, 1

• The 60-minute infusion has significantly less variability (19% coefficient of variation) compared to 15-minute (52%) or 30-minute (35%) infusions 3
• Normal GBEF is ≥38% (first percentile) or ≥49% (fifth percentile) 3, 1
• CCK/sincalide is NOT used for acute cholecystitis evaluation—it is reserved for functional gallbladder disorder and chronic acalculous cholecystitis assessment 1
• Only 2 of 60 subjects reported nausea or cramping with the 60-minute infusion compared to higher rates with shorter infusions 3

Diagnostic Performance

HIDA scan has the highest sensitivity (84.2%) for acute cholecystitis compared to ultrasound (67.3%) and CT (59.8%), though clinical utilization is limited by required resources and time. 3

• Specificity ranges from 66.8-79% for acute cholecystitis 3
• HIDA should be reserved for selected patients when ultrasound is equivocal and clinical suspicion remains high 3, 5

Special Populations and Precautions

Impaired Hepatic Function:

• Elevated serum bilirubin increases renal excretion of Tc-99m HIDA agents and delays hepatobiliary transit 2
• In patients with mean bilirubin of 9.8 mg/dL, urinary excretion increases from 1% to 3% in first 3 hours and 14.9% over 3-24 hours 2
• Blood pool activity at 10 minutes may be twice as high or more in jaundiced patients 2
• Image quality frequently diminishes in jaundiced patients, and HIDA has qualified value beyond bilirubin levels of 5 mg% 6

Impaired Renal Function:

• No specific dose adjustments are provided in guidelines, as renal excretion is minimal (1% in first 3 hours) in patients with normal hepatobiliary function 2
• Renal excretion increases with elevated bilirubin but remains a minor pathway 2

Pregnancy:

• Sincalide is contraindicated in pregnancy as it may stimulate preterm labor 3
• Ultrasound is mandatory first-line imaging throughout pregnancy, followed by MRI/MRCP without gadolinium if needed 5
• HIDA should only be used in pregnancy if ultrasound and MRI are equivocal or unavailable AND the diagnosis would significantly alter management affecting maternal or fetal outcomes 5

Absolute Contraindications

• Known allergic reaction to sincalide 3
• Intestinal obstruction 3
• Pregnancy (for sincalide administration) 3

Common Pitfalls to Avoid

• Do not perform HIDA in hospitalized or acutely ill patients for functional gallbladder assessment, as illness and medications spuriously decrease GBEF 3
• Do not use CCK/sincalide when evaluating for acute cholecystitis—it is only for functional disorders 1
• Do not interpret non-visualization at 60 minutes as diagnostic without confirming adequate patient preparation (fasting, medication restrictions) 3
• Do not proceed with HIDA in pregnancy when MRI/MRCP can provide needed diagnostic information 5