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 primarily 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 condition, such as systemic lupus erythematosus (SLE), rheumatoid arthritis, or pernicious anaemia, develops symptoms that suggest thyroid involvement. This involvement may occur at any time during the course of the other condition(s).

If a pregnant woman has a known autoimmune thyroid disease (such as Hashimoto’s thyroiditis or Graves’ disease) or has another autoimmune disorder and thyroid involvement is suspected, then one or more of the thyroid antibodies may be requested early in the pregnancy and then again near the end. These tests are used to help the doctor determine whether the baby may be at risk of thyroid dysfunction since thyroid antibodies can cross the placenta and cause 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 a variety of thyroid diseases.

Thyroid cancer is a very rare tumour, and thyroid antibodies can sometimes be detected at low level.

Significantly increased concentrations most frequently indicate thyroid autoimmune diseases such as Hashimoto’s thyroiditis, primary myxoedema, and Graves’ disease. In general, the higher the level, the more likely autoimmune thyroid disease is present. All of these antibodies, if present in the mother, can increase 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 tends to increase 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 may 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, hence why they must be requested and interpreted together. If TgAb or thyroglobulin is being used as a monitoring tool and has stayed high or dropped low initially but is increasing over time, then it may be that the treatment has not been effective and the condition is continuing or recurring. If levels are falling and/or have fallen to low or undetectable levels, then it is more likely that the therapy has been effective.

There are a variety of different methods available for measuring thyroid antibodies, and different laboratories may use different methods, which may measure slightly different things. As a result of this, different laboratories may quote different reference ranges for resultsIf you are having serial testing done (for monitoring purposes), it is therefore important to have testing done by the same laboratory using the same method.

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.