What are Hot and Cold Thyroid nodules?

As already discussed previously, thyroid cells take up iodine in order to make the thyroid hormones. This physiological activity is taken advantage of when a radioactive iodine scan is performed. The thyroid cells will take up the iodine and will produce an image of the thyroid on an X-ray film.

If a nodule is not producing thyroid hormones then it will not take up significant amounts of radioactive iodine and will appear 'cold' on the X-ray. A nodule that is actively producing hormone will take up the radioactive iodine and appear darker 'hot' on the X-ray film. Almost all 'hot' nodules are benign. Nodules detected by radioactive iodine scans are classified as cold, hot or warm. 80% of thyroid nodules are cold, 15% are warm, and 5% are hot.