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Radioiodine I-123

Getting a radio iodine I-123 scan and uptake test

Getting a Radioiodine I-123 Scan and Uptake Test

If you have symptoms of hyperthyroidism, such as weight loss, nervousness, palpitations, or heat intolerance, your healthcare provider may order a I-123 scan and uptake test to evaluate your thyroid function. This molecular radiology test uses a small amount of radioactive iodine (I-123) which is a radiopharmceutical that can help measure how much iodine your thyroid gland absorbs from your blood. This can allow your medical team to diagnose the cause of your hyperthyroidism and guide the treatment options.

The radioiodine I-123 scan and uptake test is also sometimes recommended for diagnosis when hypothyroidism (low thyroid) is suspected.

The radioiodine I-123 scan and uptake test consists of two exams that use the same radiopharmaceutical, radioiodine I-123. You take only one dose for both exams.

  • You will come to one of ARA’s imaging centers that performs nuclear medicine procedures where you will be given a pill that contains radioiodine I-123 and asked to swallow it with water. The pill is safe and has no side effects.
  • You will be asked to return to the molecular radiology department at Midtown after 4 hours for the first uptake measurement. A device called a gamma probe will be placed over your neck to detect how much I-123 your thyroid gland has absorbed. The procedure is painless and takes about 15 minutes.
  • You will return to the imaging center again after 24 hours for the second uptake measurement. The same procedure will be repeated using a gamma probe.
  • During this visit you will also get a second scan using a gamma camera. You will lie down on a moveable examination table with your head tipped back slightly and the gamma camera will take a series of images of the thyroid gland. You will need to be still while the images are taken. Scanning time is usually 30 minutes or less.
  • You will need to drink plenty of fluids and urinate frequently to flush out the I-123 from your body. The radiation exposure from the test is very low and poses little or no risk to you or others.
  • You will need to stop taking certain medications that can interfere with the test results, such as thyroid hormones, antithyroid drugs, or iodine-containing supplements. Your healthcare provider will tell you when to stop and resume these medications.
  • You will need to fast for at least 4 hours before the test.
  • You will need to inform your healthcare provider if you are pregnant, breastfeeding, or have any allergies.
  • You will also need to let your healthcare provider know if you have had any CT scans using iodine-based contrast within the past several months.


  • Molecular radiology scans can give your medical team information that no other exam can supply. The radioiodine I-123 scan and uptake test is targeted to show information about your thyroid’s size, shape, position, and function because of the thyroid’s ability to pull iodine out of your bloodstream.
  • Molecular radiology exams often take the place of open exploratory surgery. As such, they are less expensive and less invasive for the patient.


  • The radioactivity in a radioiodine I-123 scan and uptake test is low and the benefits of the exam are considered to far outweigh the very low risk.
  • Discuss with your healthcare provider and ARA scheduler any allergies you may have, especially to iodine, to avoid any chance of an allergic reaction. If a reaction should occur, your ARA team is experienced in responding.
  • Be sure and let your healthcare provider and molecular radiology team know if there is any chance you might be pregnant, or if you are breastfeeding.

Your healthcare provider will refer you to ARA, either by giving you a paper referral or through an electronic medical system. You should receive an automated call from ARA if your referral is sent electronically. Please call (512) 453-6100 to schedule your appointment.

A radiologist who is trained to interpret molecular radiology examinations will analyze the images and send a report to the healthcare provider who referred you to ARA. Your provider will then share the results with you.