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What is a thyroid scan?

A thyroid scan is a test that uses radioactive tracers to observe the function and structure of thyroid gland. The test also shows the shape, location and size of thyroid gland and is typically recommended with a radioactive iodine uptake test for accurate results.

  1. Why is thyroid scan performed?
  2. How do you prepare for thyroid scan?
  3. How is thyroid scan performed?
  4. What do thyroid scan results mean?

Thyroid scan helps evaluate the following:

  • Examine thyroid nodules
  • To detect the presence of thyroid cancer
  • Evaluate goitre (enlargement of the thyroid gland)
  • To identify the cause of an overactive thyroid gland
  • Detect any problems in thyroid gland
  • To check if thyroid cancer has spread outside the thyroid gland
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Individuals might be asked to have a low-iodine diet for many days before the test or stop taking any supplements or medicines before undergoing the test. They will be asked to remove dentures and jewellery pieces just before the scan.

It is important to inform the healthcare provider about the names and doses of medications that the individual is taking regularly. This is because, certain medicines like antithyroid medicines, thyroid hormones and supplements that have iodine may interfere with test results. Individuals should also inform the doctor about allergies to medications, especially medications containing iodine, and any severe allergy to a substance. Additionally, the physician should know if you have undergone any tests that included iodine dye or radioactive materials, like CT scan, 4 weeks before thyroid scan. Women should inform if they are pregnant, suspect pregnancy or are breastfeeding.

Individuals will either be injected with technetium (radioactive label) about 30 minutes before the scan or will be asked to swallow iodine about 4 to 24 hours before the scan.

The following steps are followed while performing thyroid scan:

  • The individual is asked to lie down on his/her back with their neck extended, and head leaned backwards
  • A gamma scintillation camera is used to take pictures of the thyroid gland from three different angles
  • The camera scans the body from head to toes if a complete-body thyroid scan has been ordered
  • Another scan may be done after 30 minutes or after 24 hours

There are no risks associated with a thyroid scan. Only a minimal amount of radioactive material is used in this test; therefore, the chances of side effects due to it are very less. However, special precautions are to be taken while urinating as the radioactive material used in the test flushes out via urine within the next 24 hours. Individuals will be asked to flush the toilet twice and wash their hands thoroughly after urinating.

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Normal results:

In a normal thyroid scan, thyroid gland appears in the correct location and in its normal size and shape. The gland appears as an even grey-coloured organ without lighter or darker areas.

Abnormal results:

An abnormal thyroid scan could mean the following:

  • A sign of tumour if the thyroid appears to be pushed off to one side or enlarged
  • The possibility of a problem in thyroid gland if one part of the gland appears lighter in colour
  • An overactive thyroid if nodules of thyroid gland appear darker
  • A darker thyroid can also indicate inflammation or other damage to the organ
  • Hot nodules, indicating excess thyroid hormone production in the nodule if the thyroid is overactive
  • Cold nodules, indicating no thyroid hormone production in the nodule if the thyroid is underactive

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


  1. Michigan Medicine: University of Michigan [internet]; Thyroid Scan
  2. Salvatore D, Davies TF, Schlumberger M-J, Hay ID, Larsen PR. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 13th ed. Philadelphia, PA: Elsevier; 2016:chap
  3. Blum M. Thyroid imaging. In: Jameson JL, De Groot LJ, de Kretser DM, et al., eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016: chap 79.
  4. National Institute of Health. US National Library of Medicine [internet]: Bethesda (MA), US. US Department of Health and Human Services Procedures/Diagnostic Tests: Thyroid scan/thyroid uptake study
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