Thyroglobulin antibodies (TgAb, anti-Tg)

Thyroglobulin antibodies (TgAb, anti-Tg) are autoantibodies against thyroglobulin, the storage protein of the thyroid. They are measured in serum. In the autoantibody screens for long/post-COVID and chronic fatigue syndrome they appear as “TG” together with TPO antibodies and other autoantibodies. Important: the same abbreviation “TG” stands for triglycerides, i.e. blood fats, in clinical chemistry profiles – that is an entirely different value. Thyroglobulin antibodies show whether the immune system is turning against the thyroid and are usually considered together with TPO antibodies and the thyroid hormones.

What thyroglobulin does in the body

Thyroglobulin is a very large protein that the thyroid cells make and release into the inside of the follicles. There it serves as a scaffold for hormone formation: thyroid peroxidase incorporates iodine into its tyrosine building blocks and links them to form thyroxine (T4) and triiodothyronine (T3), which initially remain bound in thyroglobulin. This creates a hormone store for weeks. When needed, the thyroid cells take the protein back up, split off the hormones and release them into the blood. Small amounts of thyroglobulin also enter the blood themselves, where the immune system encounters them.

Low thyroglobulin antibodies – what does it mean?

A low or undetectable value is the normal case. It speaks against the immune system forming antibodies against the storage protein of the thyroid. On its own, however, it does not rule out an autoimmune thyroid inflammation, because many of those affected mainly have TPO antibodies. Both antibodies are therefore usually determined together and interpreted together with TSH and the free thyroid hormones. After treatment for thyroid cancer a low value plays a special role: thyroglobulin itself can then be measured reliably as a follow-up value, because no antibodies interfere with the measurement.

Raised thyroglobulin antibodies – what happens in the thyroid?

Raised values show that the immune system recognises thyroglobulin as foreign. They occur mainly in Hashimoto's thyroiditis and Graves' disease, usually together with TPO antibodies. Immune cells migrate into the thyroid and damage the tissue over years, so that hormone production can decline and an underactive thyroid can develop. Thyroglobulin antibodies are considered less specific than TPO antibodies; isolated raised values are also found in people without symptoms, more often in women and with increasing age. Population studies have observed that they occur more often after a marked increase in iodine intake, because more heavily iodinated thyroglobulin is more conspicuous to the immune system.

The interpretation is given in your report.