A Hepatobiliary Iminodiacetic Acid (HIDA) scan is a specialized nuclear medicine procedure used to visualize the function of the biliary system. This diagnostic tool tracks the flow of bile from the liver, through the bile ducts, into the gallbladder, and into the small intestine. By injecting a small amount of radioactive tracer, the procedure helps assess potential blockages, leaks, or signs of inflammation. This imaging technique offers functional insight, aiding in the diagnosis of conditions like acute inflammation of the gallbladder or bile duct obstruction.
Fasting and Hydration Guidelines
The direct answer to whether you can drink water before a HIDA scan is yes, but this allowance is specific to plain water only. Patients must refrain from eating or drinking anything else for a minimum fasting period, which commonly ranges from four to twelve hours depending on the facility’s protocol. It is acceptable to drink clear water to stay hydrated, and a small sip may be used to swallow necessary medications. All other beverages, including coffee, tea, juice, and soda, must be avoided because they can trigger a physiological response that interferes with the scan’s accuracy. Furthermore, certain medications, particularly opiate-based pain relievers, must often be withheld, sometimes up to 24 hours, as they can affect the bile ducts and skew the test results. Patients should always confirm their exact preparation instructions with the ordering physician or the imaging facility.
Why Preparation is Essential for Accurate Results
The necessity of fasting is rooted in the normal physiology of the digestive system, which directly involves the gallbladder. When a person eats, especially a meal containing fat, the body releases the digestive hormone called cholecystokinin (CCK). This hormone signals the gallbladder to contract and release its stored bile into the small intestine to aid in digestion. If the gallbladder is already contracted and empty before the HIDA radiotracer is injected, the tracer will be unable to enter and fill the organ. Failure of the gallbladder to fill is often interpreted as a sign of obstruction or acute disease. This would lead to a false-positive result, indicating a problem where none exists, simply because the gallbladder was emptied by a recent meal. Therefore, the fasting period ensures the gallbladder is in a relaxed, distended state, allowing the radioactive tracer to enter and accumulate within it. Fasting for too long (more than 24 hours) can also be problematic because stagnant bile thickens, which can prevent the tracer from entering. This balance is maintained by the required fasting window of four to twelve hours, which optimizes the gallbladder’s readiness for the test.
Steps of the HIDA Scan Procedure
Once the patient arrives for the procedure, a technician inserts an intravenous (IV) line, usually in the arm. Through this IV, a small dose of the radioactive tracer is injected, which travels through the bloodstream to the liver. The liver cells absorb the tracer, incorporate it into the bile, and then secrete it into the biliary system. The patient is positioned beneath a gamma camera, which detects the energy emitted by the radiotracer as it moves through the organs. This camera takes a series of images over a period that typically lasts between one and four hours, depending on how quickly the tracer progresses. The initial imaging tracks the path of the tracer from the liver into the bile ducts and the gallbladder, which should normally be visible within one hour. When assessing the rate at which the gallbladder empties, a synthetic version of the hormone CCK, such as sincalide, is administered through the IV during the procedure. This injection stimulates the gallbladder to contract, allowing the technician to calculate the Gallbladder Ejection Fraction (GBEF). The patient may feel temporary abdominal cramping or discomfort during this part of the test.