Thyroid Antibodies

Thyroid antibody testing may be used to help investigate the cause of an enlarged thyroid gland (goitre) and/or performed as a follow-up when other thyroid test results (such as free T3, free T4, and/or TSH) show signs of thyroid dysfunction. Antibody testing is normally requested to help diagnose an autoimmune thyroid disease and to separate it from other forms of thyroiditis and thyroid disease.

Thyroid antibody tests may also be requested if a person with a known non-thyroid-related autoimmune conditions, such as systemic lupus erythematosus (SLE), rheumatoid arthritis, or pernicious anaemia, develops symptoms that may suggest a change in how the thyroid gland is working. This is important as despite these autoimmune conditions not directly affecting the thyroid gland, they can increase the risk of developing autoimmune thyroid disease in the future.

If a pregnant woman has a known autoimmune thyroid disease (such as Hashimoto thyroiditis or Graves disease) or has an existing autoimmune condition associated with a higher chance of developing thyroid disease, then one or more of the thyroid antibodies may be requested. This normally occurs once at the early stages of pregnancy and is repeated near the end. These tests are used to help the doctor determine whether the baby may be at risk of thyroid dysfunction. This is important as thyroid antibodies from the mother can cross the placenta and increase the risk of hypothyroidism or hyperthyroidism in the foetus or newborn.

Thyroid antibody testing may also be requested when a patient is being investigated for infertility.

Mild to moderately elevated levels of thyroid antibodies may be found in association with a variety of diseases, and must be interpreted in combination with symptoms and other thyroid hormone tests to diagnose autoimmune thyroid disease.

Thyroid antibodies can sometimes be slightly increased in thyroid cancer, but this is a rare cause of detectable thyroid antibodies.

Significantly increased thyroid antibody concentrations most frequently indicate thyroid autoimmune diseases such as Hashimoto thyroiditis, primary hypothyroidism, and Graves disease. In general, the higher the level, the more likely autoimmune thyroid disease is present. If present in the mother, thyroid antibodies are associated with an increased the risk of hypothyroidism or hyperthyroidism in the foetus or newborn.

Thyroid antibodies can also be found in other autoimmune disorders, such Type 1 diabetes, pernicious anaemia, rheumatoid arthritis, and SLE.

A certain percentage of patients who are healthy may be positive for one or more thyroid antibodies. The prevalence of thyroid antibodies tends to be higher in women and increases with age. If a person with no apparent thyroid dysfunction has a thyroid antibody present, the doctor will track health over time and monitor thyroid function tests (TSH, FT4 and sometimes FT3). While most will never experience thyroid dysfunction, a few patients may develop it in the future.

Monitoring of thyroid cancer
TgAb and thyroglobulin can be used in in the monitoring of certain types of thyroid cancer. TgAb can sometimes, for technical reasons, interfere with the test results for thyroglobulin which means that both tests should be requested and interpreted together. If TgAb and thyroglobulin are being used to monitor thyroid cancer, then high levels or increases over time may lead to further investigation of how well the treatment is working or whether the cancer has reoccurred. If levels are falling and/or have fallen to low or undetectable levels, then it is more likely that treatment has been effective.

There are a variety of methods available for measuring thyroid antibodies, and different laboratories may not use the same method leading to slight differences in results. Therefore, if you are having repeated thyroid antibody tests for monitoring purposes, it is important that this is done using the same method and ideally by the same laboratory. Using the same method every time means that results can be directly compared against each other, which is essential for effective monitoring. The variation between methods also means that slightly different reference ranges may be quoted when laboratories report results.

There are a few lifestyle changes that can prevent or eliminate thyroid antibodies. It is important for patients and their doctors to be aware of them when they are present, so that appropriate clinical decisions can be made.