Thyroglobulin

In someone with an intact thyroid the range is roughly 3.5 to 77 ug/L, but after the thyroid has been removed for cancer the expected value is undetectable and the lab prints a much lower cut-off.

Thyroglobulin is the large protein made only by thyroid cells, in which thyroid hormone is built and stored. A small amount leaks into the blood in everyone with a thyroid gland. After the gland has been removed for thyroid cancer, the level should be very low, so it is used as a marker for any remaining thyroid tissue.

It is mainly requested as a follow-up test after treatment for thyroid cancer, usually alongside thyroglobulin antibodies. It is occasionally used to look at the cause of an overactive thyroid or in babies born with an absent thyroid.

• Any thyroid tissue that remains or has returned after thyroid cancer surgery
• An enlarged thyroid (goitre) or thyroid nodules
• An overactive thyroid, including Graves disease and thyroiditis
• Recent thyroid biopsy, surgery or radioiodine
• Pregnancy, in the general population

• Removal of the thyroid gland, where an undetectable level is expected
• Thyroglobulin antibodies in the blood, which make the assay read falsely low
• Taking thyroid hormone in amounts that switch off TSH, which reduces thyroglobulin production

• Thyroglobulin antibodies can make the reading falsely low on most assays
• Recent thyroid surgery, biopsy or radioiodine can raise it for a few weeks
• Different assays give different numbers, so follow-up is best done in the same laboratory

No fasting needed. After thyroid cancer, the trend over time in the same laboratory, always read with the antibody result, is what matters. Some reports are 'stimulated' values taken after TSH injection or stopping thyroid hormone.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.