What is a Thyroid Scan?

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  • Written By: Emma Lloyd
  • Edited By: Bronwyn Harris
  • Last Modified Date: 11 September 2019
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A thyroid scan, also called a thyroid scan and radioactive iodine uptake test or simply a thyroid uptake test, is a type of nuclear imaging test. During this test a small amount of radioactive material is used to help diagnose diseases of the thyroid gland. The test itself is simple, but must be performed over two days to get accurate information about the thyroid.

Nuclear imaging tests are those which use small amounts of radioactive material to act as a “tracer” inside the body. In the case of a thyroid uptake test, the material used is radioactive iodine. Several hours before the scan, the patient ingests a carefully measured amount of radioactive iodine, and this material is used within the body as normal iodine would be. The material is taken up by the thyroid gland, and can then be assessed by equipment that detects radioactive material.

Thyroid scans are used to determine whether the thyroid gland is working normally. An underactive or overactive thyroid will take up less or more iodine, respectively, and this can be detected by the scan. A thyroid uptake scan can also detect the size of the thyroid gland and whether any lumps have formed within the gland which might indicate the presence of cancer.


Prior to undergoing a thyroid scan, a patient should ensure his or her doctor has their full medical history. This includes information about medications the patient is taking and whether they have any allergies. Women who are pregnant or are breastfeeding should inform their doctor, as the scan can be harmful to fetal development.

The thyroid scan is carried out in three stages. The first stage is swallowing a small pill which contains radioactive iodine. This is usually carried out in the morning. Between four and six hours later, a scan is carried out to detect traces of radioactive iodine in the thyroid. The third and final stage, a second thyroid scan, is carried out the next day.

During the scan, the patient lies on his or her back, underneath the scanning equipment. The equipment is calibrated to detect radioactive iodine, and passes over the patient to detect the location of radioactive iodine within the body. This information is then transferred to a computer, which generates images of the thyroid gland, showing where the iodine is located. These images can be interpreted by a doctor to determine the size of the gland, and how well it is functioning.

There are certain risks associated with undergoing a thyroid uptake scan. The radiation risk is extremely low, as the amount of radioactive iodine used is minimal. The greatest risk to the patient is that of allergies to drugs that are used in the procedure. For women, there is an additional risk of harm to an unborn or breastfeeding baby.


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