A Hepatobiliary Iminodiacetic Acid scan (HIDA scan) is a medical imaging procedure used to evaluate the function of the liver, bile ducts, and gallbladder. This diagnostic tool is effective for identifying issues like inflammation, blockages, or leaks within the biliary system. Because the test involves a small radioactive substance, patients often seek to understand its safety profile. The HIDA scan is generally considered safe, and the benefits of an accurate diagnosis usually outweigh the minimal risks.
Understanding the Procedure and the Tracer Used
The HIDA scan is a nuclear medicine test that uses a radioactive tracer to create images of internal organ function. The procedure begins with the injection of a small amount of a radiotracer, typically a Technetium-99m labeled compound, into a vein. This compound mimics bilirubin, allowing it to be absorbed by liver cells, mixed with bile, and secreted into the bile ducts and gallbladder. A gamma camera detects the tracer’s movement, allowing physicians to observe the real-time function of the organs. Technetium-99m is chosen because its short half-life of just over six hours ensures the radioactive material decays quickly and is eliminated from the body within a day or two.
Immediate Safety Concerns and Minor Side Effects
Immediate safety concerns associated with a HIDA scan are typically minor and unrelated to radiation exposure. The most common reaction is slight pain, bruising, or swelling at the intravenous injection site, which resolves quickly. Mild allergic reactions to the radiotracer are possible but very rare. Sometimes, a drug like cholecystokinin (CCK) is administered during the test to stimulate gallbladder contraction. This drug may cause temporary side effects such as nausea, abdominal discomfort, or flushing, but these effects are mild and distinct from the radioactive component.
Radiation Exposure Levels and Comparative Risk
The most common concern regarding a HIDA scan is the exposure to ionizing radiation. The radiation dose typically falls within the range of 2.5 to 4 millisieverts (mSv), which is comparable to the average natural background radiation exposure received in one year (around 3.6 mSv in the United States). The risk of long-term harm, such as cancer, from this level of exposure is considered negligible compared to the diagnostic benefit. For context, this dose is lower than that of a chest CT scan, which often ranges from 5 to 8 mSv. Furthermore, the radioactive material’s short half-life ensures that the patient’s exposure is contained to a brief period, and the substance quickly leaves the body through natural waste processes.
Patient Conditions That Prevent the Scan
While the HIDA scan is generally safe, certain patient conditions make the procedure inappropriate or require special precautions. The most significant contraindication is pregnancy, as the radioactive tracer could potentially expose the developing fetus. Women who are pregnant or suspect they might be pregnant must inform their healthcare provider before the scan is performed. Patients who are breastfeeding must also take precautions because the tracer can pass into breast milk, requiring them to pump and discard breast milk for at least 24 hours following the injection. Furthermore, patients with very severe liver dysfunction, indicated by extremely high bilirubin levels, may not be suitable for the test, as the liver may not be able to process the radiotracer effectively.