A Hepatobiliary Iminodiacetic Acid (HIDA) scan is a common nuclear medicine imaging procedure used to assess the function of the liver, gallbladder, and bile ducts. The scan tracks the flow of bile from the liver into the small intestine, helping physicians diagnose issues like blockages or inflammation. Accurate results depend on proper preparation, including specific consumption guidelines. Following these instructions ensures the procedure is successful and provides helpful information to your healthcare team.
Fasting Rules and Drinking Water
The primary instruction for a HIDA scan is complete fasting from food, typically for four to twelve hours before the procedure. This fast includes all solid foods and any beverages other than plain water, ensuring the digestive system is inactive. The exact duration varies, so confirm the required time with your provider.
Plain water is generally permitted and encouraged for hydration up until two hours before the scheduled scan time. However, beverages like coffee, tea, juice, milk, or soda are strictly prohibited because they stimulate the digestive system. Fasting also means avoiding anything that triggers bile release, such as chewing gum, hard candies, or ice chips, as these can compromise the test’s accuracy.
Why Strict Preparation is Necessary
Strict fasting is necessary because the HIDA scan relies on the gallbladder being relaxed and relatively full. The scan uses a radioactive tracer that mimics bile, traveling from the liver, through the bile ducts, and into the gallbladder for storage.
Consuming anything other than water triggers the release of cholecystokinin (CCK). CCK signals the gallbladder to contract forcefully, emptying its stored bile into the small intestine to aid in fat digestion. If the gallbladder is contracted due to recent food intake, it will not fill properly with the tracer. This leads to inaccurate or inconclusive results, potentially mimicking a blockage and necessitating a repeat scan. The fasting window ensures the gallbladder is relaxed, allowing it to take up the tracer and accurately assess its function.
The Steps of the HIDA Scan Procedure
The HIDA scan begins after you arrive and change into a gown, ensuring no metal objects interfere with the imaging equipment. A technologist places an intravenous (IV) line for the injection of the radiotracer, often Technetium-99m labeled iminodiacetic acid. This substance is tracked throughout your biliary system.
Once injected, you lie still on an examination table while a specialized gamma camera is positioned close to your abdomen. The camera detects the tracer’s gamma rays as it moves from the liver, into the bile ducts, and eventually into the gallbladder and the small intestine. In a healthy system, the tracer should reach the gallbladder within about 60 minutes.
If the doctor needs to assess gallbladder function, a synthetic version of CCK, called sincalide, may be administered via the IV. This stimulates the gallbladder to contract, allowing the technician to measure the percentage of bile ejected, known as the Ejection Fraction. The entire imaging process typically takes 60 to 90 minutes, though it may last up to four hours if delayed images are required.
Preparation Beyond Food and Drink
Beyond dietary restrictions, other preparation steps ensure a smooth and accurate HIDA scan. Discuss all current medications and supplements with your ordering physician before the test date. Certain pain medications, particularly opioids, can cause the sphincter of Oddi—a muscle controlling bile flow—to contract. This contraction could interfere with the scan results and mimic a blockage.
Your doctor may instruct you to temporarily stop specific medications before the scan. On the day of the procedure, wear loose, comfortable clothing and remove all metal jewelry or accessories from the chest and abdominal area. Remember to bring your photo identification, insurance card, and necessary paperwork.