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Thyroid Scan

What is a thyroid scan?

A thyroid scan is a procedure in which your healthcare provider examines your thyroid gland using radioactive iodine. The radioactive iodine is detected by an instrument called a scanner. The scan helps your provider see how well the gland is working.


The thyroid gland is a small gland at the lower front of the neck. It makes hormones that control your metabolism, which is the rate at which your body's cells perform their functions. The thyroid gland is critical for maintaining body temperature and controlling heart rate, appetite, and digestive tract function.

When is it used?

This procedure is used to diagnose problems with the thyroid gland. The thyroid scan provides information on how the gland is functioning. Depending on the problem and your condition, you may have other tests, such as a CT scan (a special type of X-ray test) or an ultrasound scan (using sound waves).

How do I prepare for a thyroid scan?

Your healthcare provider will give you capsules containing a radioactive chemical (often iodine). You will swallow these capsules 4 to 24 hours before the test. Tell your provider if you are allergic to shellfish or other things that contain iodine. Also, tell your provider if you have had other contrast-dye tests done in the past few months such as a CT scan.

What happens during the procedure?

After taking the capsules, you will lie on an examining table while a scanner is held near your neck. The scanner measures the amount and distribution of radiation in the thyroid. This information will help your healthcare provider understand how well the thyroid is working. You may have more than one scan done. Your provider may also use a scanning device that produces a picture of the thyroid gland, showing areas where there may be a problem.

What happens after the procedure?

Your healthcare provider will give you the test results when the complete report is available. You can go home after the test is completed.


Ask your healthcare provider what other steps you should take and when you should come back for a checkup.

What are the benefits of this procedure?

This test is painless and helps your healthcare provider make a more accurate diagnosis.

What are the risks of this procedure?

The amount of radioactivity given in this test is so small that it does not pose a risk.


You could be allergic to the dye. You should ask your healthcare provider how this risk applies to you.

When should I call my healthcare provider?

Call your healthcare provider right away if you develop a skin rash after the test.


Call your provider during office hours if:

  • You have questions about the procedure or its result.
  • You want to make another appointment.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.


HIA File diag5132.htm Release 13/2010

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