Thyroglobulin antibodies (anti-Tg)

Cut-offs depend on the assay (for example below 115, below 40 or below 4.5 kIU/L), so the lab's own printed cut-off is the one to use.

Thyroglobulin is the protein the thyroid uses to store and make its hormones. Anti-thyroglobulin antibodies are immune proteins directed against it. They are found in autoimmune thyroid disease, usually alongside anti-TPO antibodies, and they matter after thyroid cancer surgery because they can interfere with the thyroglobulin test used for follow-up.

It is requested with anti-TPO when autoimmune thyroid disease is being looked into, and routinely alongside every thyroglobulin measurement after treatment for thyroid cancer, because the antibody can make thyroglobulin read falsely low.

• Autoimmune thyroid disease, both underactive and overactive forms
• Other autoimmune conditions
• Female sex and older age, in the general population
• Some thyroid cancers, where the level is followed after treatment

• A value below the cut-off is the expected finding
• After complete removal of thyroid tissue the level tends to fall over one to three years
• Assay differences, so a change between laboratories may not be real

• Some healthy adults, more often women, have a positive result with a normal thyroid
• Different assays give different numbers, so results from two labs are not directly comparable

No fasting needed. After thyroid cancer treatment it is measured with thyroglobulin each time, and the trend matters more than a single number.

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