Thyroid scan



Thyroid scans are functional tests that assess the activity of thyroid gland. Earlier, thyroid scans were done with radioactive iodine. This has largely been replaced by technetium (Tc- 99m) pertechnetate, which involves a much lower radiation dose and costs considerably less.


  • Hot nodule: Increased uptake of iodine
  • Cold nodule: Decreased uptake of iodine.

Important abnormalities:

  1. Diffusely increased uptake: Grave’s disease
  2. Diffusely decreased uptake: Thyroiditis
  3. Single hot nodule: Solitary toxic nodule
  4. Multiple hot & cold nodules: Toxic multinodular goiter/ Plummer’s disease.

MCQ [Reference: 27th Bailey]:

  • Risk of malignancy in a hot nodule is 4%
  • Risk of malignancy in a cold nodule is 20%.


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