TgAb (thyroglobulin antibodies)

TgAb - thyroglobulin antibodies, also written anti-Tg or anti-thyroglobulin - are autoantibodies produced by the immune system against thyroglobulin, the protein thyroid cells use to make and store thyroid hormone.

In clinical practice, TgAb are primarily relevant to thyroid cancer follow-up. After a total thyroidectomy and radioactive iodine ablation, thyroglobulin (Tg) is used as a surveillance marker - it should be very low or undetectable if no thyroid tissue remains. However, when TgAb are present, they can interfere with the Tg assay and make the result unreliable, either falsely lowering or masking a rise in Tg that might indicate residual or recurrent disease.

For this reason, TgAb are routinely measured in the same blood draw as Tg during thyroid cancer monitoring. A rising TgAb level over serial measurements can itself be a signal worth investigating, even when the Tg result appears reassuringly low.

TgAb are also found in some people with autoimmune thyroid conditions such as Hashimoto's thyroiditis or Graves' disease, but they are not a first-line diagnostic test for those conditions. TgAb are non-diagnostic on their own - interpreting them in context is a task for your specialist or clinical team.