HIDA Scan NPO Requirements
Yes, patients must be NPO (fasting) for at least 4-6 hours before a HIDA scan, with overnight fasting being optimal. 1
Fasting Requirements
Patients should fast for a minimum of 4 hours, though 4-6 hours is preferred, with overnight fasting being the optimal preparation. 1, 2
The fasting requirement ensures adequate gallbladder filling with bile, which is essential for accurate interpretation of the scan. 2
One study specifically evaluated patients who had fasted for more than 8 hours before CCK-HIDA scanning, though this extended duration is not universally required. 3
Rationale for NPO Status
Fasting allows the gallbladder to fill with hepatobiliary radiotracer, which is necessary to visualize the gallbladder and assess for cystic duct obstruction in acute cholecystitis. 2
If a patient has recently eaten, the gallbladder may have already contracted and emptied, potentially leading to false-positive results (non-visualization of the gallbladder despite a patent cystic duct). 2
Important Medication Restrictions
Beyond NPO status, several medications must be withheld to avoid false results:
Opiates must be withheld for at least 48 hours before HIDA scanning because they cause sphincter of Oddi spasm and can spuriously decrease gallbladder ejection fraction, leading to false-positive results. 1, 2
Anticholinergic drugs must be withheld for at least 48 hours as they directly impair gallbladder contraction. 1
Other medications to avoid within 24 hours include nifedipine, indomethacin, octreotide, theophylline, benzodiazepines, phentolamine, isoproterenol, and progesterone. 1
Nicotine and alcohol should also be avoided prior to testing. 1
Special Considerations for Prolonged NPO/TPN Patients
Patients on prolonged fasting (>5 days) or total parenteral nutrition (TPN) can still undergo HIDA scanning with acceptable accuracy. 4
One study found that 78% of patients on TPN and 75% of patients who were NPO for at least 5 days had normal hepatobiliary scintigraphy, suggesting a lower false-positive rate than previously reported. 4
The standard 4-6 hour fast remains appropriate even for critically ill patients, and pre-treatment with CCK is generally not required for acute cholecystitis evaluation. 4
Common Pitfalls to Avoid
Do not pre-empty the gallbladder with CCK before the scan when evaluating for acute cholecystitis, as this decreases test specificity; if CCK is inadvertently given, wait at least 4 hours before beginning the HIDA study. 2
Ensure careful drug history, especially regarding opiates, as these medications circulate for many hours and can affect results even if discontinued shortly before the scan. 2
For post-bariatric surgery patients, protocol modifications may be needed, including longer scan duration (75-90 minutes) and addition of SPECT/CT for anatomical localization. 5
Role of CCK in HIDA Scanning
CCK is NOT used during standard HIDA scans for acute cholecystitis; it is reserved for functional gallbladder disorder (biliary dyskinesia) evaluation where gallbladder ejection fraction measurement is needed. 1, 6
When CCK is used for functional assessment, sincalide is administered at 0.02 μg/kg infused over 60 minutes after gallbladder filling is documented. 6