What is thyroglobulin?

Thyroglobulin is a protein produced by normal thyroid tissue. It serves an important function in the synthesis of thyroid hormone produced by the thyroid gland. The level of thyroglobulin present in the body can be measured with blood tests. Thyroid cancer cells may continue to produce thyroglobulin, even after undergoing changes that lead to unrestricted growth and spread to other parts of the body. Thyroglobulin levels may be markedly elevated in patients with active thyroid cancer.

Theoretically, a patient who has undergone thyroid surgery and effective treatment with radioactive iodine should not have any remaining thyroid cancer cells or normal thyroid tissue present. In such a situation, thyroglobulin should not be detectable, and blood tests checking for it should be negative. This principle enables physicians to use thyroglobulin blood tests to determine whether thyroid cancer has persisted or recurred after treatment with radioactive iodine. If thyroglobulin remains detectable after treatment with radioactive iodine, there may still be viable thyroid cancer cells present. If thyroglobulin falls to an undetectable level after treatment with radioactive iodine, it is likely that any remaining thyroid cancer cells have been destroyed. In this situation, subsequent thyroglobulin blood tests can be used to monitor a patient to determine whether thyroid cancer may have recurred. If a patient's thyroglobulin level goes from being undetectable following treatment to later become detectable at a measurable level, this may raise concern that thyroid cancer has recurred, and may prompt further evaluation as indicated.

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