A blood sample taken from a vein in your arm
These tests detect the presence and measure the quantity of specific thyroid autoantibodies in the blood. These autoantibodies are made when a person’s immune system mistakenly recognises parts of the thyroid gland or thyroid proteins as foreign (non-self) and can lead to chronic inflammation of the thyroid (thyroiditis), tissue damage, and disruption of thyroid function.
The thyroid is a small, butterfly-shaped gland that lies flat against the windpipe in the throat. The primary hormones that it produces are thyroxine (T4) and triiodothyronine (T3), which help the body to regulate the rate at which it uses energy. The body has a feedback system that utilises thyroid stimulating hormone (TSH) to turn thyroid hormone production on and off and maintain a stable amount of the thyroid hormones in the blood. When thyroid antibodies interfere with this process, it can lead to chronic conditions and disorders associated with either too little or too much of the thyroid hormones being produced and released. Hypothyroidism (not enough thyroid hormone(s)) can cause symptoms such as weight gain, fatigue, goitre (enlarged thyroid gland), dry skin, hair loss, intolerance to cold, and constipation. Hyperthyroidism (too much thyroid hormone(s)) can cause symptoms such as sweating, rapid heart rate, anxiety, tremors, fatigue, difficulty sleeping, sudden weight loss, and protruding eyes.
How is it used?
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.
When is it requested?
Thyroid Antibody Acronym Present in When ordered Thyroid peroxidase antibody/thyroid microsomal antibody TPOAb Autoimmune thyroid disease: Hashimoto thyroiditis (95%); primary hypothyroidism (90%); Graves disease (18%) When patient has symptoms or test results suggesting hypothyroidism; when a doctor is considering starting a patient on a drug therapy, such as lithium, amiodarone, interferon alpha, or interleukin-2, that has associated risks of developing hypothyroidism when TPOAb are present Thyroglobulin antibody TgAb Tested as part of monitoring of treatment for thyroid cancer. Also present in autoimmune thyroid disease. Not as reliable as TPOAb in testing for autoimmune thyroid disease. Thyroglobulin antibody together with thyroglobulin levels are used at regular intervals after thyroid cancer treatment. The presence of thyroglobulin antibodies may interfere with the test for thyroglobulin which is also tested as a tumour marker. Thyroid stimulating hormone receptor antibody TRAb Graves disease When patient has symptoms of hyperthyroidism; to monitor effectiveness of anti-thyroid therapy during treatment of hyperthyroidism
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.
What does the test result mean?
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.
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.
Is there anything else I should know?
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.
What can be done to prevent, reduce, or remove thyroid antibodies?
Are thyroid antibodies part of routine testing?