Medical Imaging

Nuclear Medicine > Exams & Procedures > Thyroid Uptake

This test determines the level of activity of the thyroid gland (such as overactive, underactive, or normal). This test also assists the doctor in calculating the dose of radioiodine to be used in the treatment of overactive thyroid (hyperthyroidism) or thyroid cancer.

The test involves the administration of a radioactive tracer that will flow through the bloodstream and be picked up by the thyroid gland. Measurements will be taken of the tracer distribution using a special detector on two separate days.

Preparation

  • This is a two-day test. You will be interviewed, given a capsule and return two hours later for a measurement. You will have the measurements repeated on the second day. Each visit lasts about 20 minutes.
  • This test is often requested in combination with a thyroid scan, which looks at the size, shape and position of your thyroid gland. The thyroid scan is performed after the second uptake visit and takes about 20 to 30 minutes.
  • Many medications interfere with the results of this test. Please talk to your doctor about which medications to stop for this test and when to stop taking them. Medications are usually stopped four weeks before this test.
  • Foods high in iodine should not be eaten from one week before the test until the test is complete. Excessive iodine in the body falsely lowers the results of this test. Do not eat or drink products that contain shellfish (lobster, crab, shrimp etc); kelp products or supplements, or cough medicines for at least one week.
  • You should have had no X-ray tests that use an iodine-based contrast dye within two to four weeks of this test.
  • Bring a list of all medications and supplements you take. This includes vitamins, herbal remedies, and holistic medications.
  • Do not bring children or pregnant women with you to the department. We do not want to expose them to unnecessary radiation.
  • Any of these procedures is subject to change according to the nuclear medicine physician. The duration of the tests is a rough estimate. Please be aware that the time may be lengthened if a scan has to be repeated, if emergency cases are brought to the department or due to unforeseen circumstances.

About the Procedure

  • The procedure takes about 15 minutes on three separate visits for the thyroid uptake only.
  • A technologist will briefly explain the test to you and try to answer any questions you may have about the procedure.
  • You will be interviewed about your thyroid condition, your medications, and any signs and symptoms you may be experiencing.
  • The technologist will give you a radioactive tracer capsule.
  • Measurements of the tracer distribution are taken two hours after the injection.
  • You will return the next day at a specified time to repeat these measurements.