Also known as: Antimicrosomal antibodies; Thyroid peroxidase antibodies; TPOAb; Anti-TPO; TBII; Thyroglobulin antibodies; TgAb; TSH receptor antibodies; TRAb;
Name: thyroid peroxidase antibodies (TPOAb); thyroglobulin antibodies (TgAb); TSH receptor antibodies; TRAb;
Related tests: T3, T4, Thyroglobulin, Thyroid antibodies, TSH
Why get tested?
To help diagnose and monitor autoimmune thyroid diseases and distinguish them from other forms of thyroiditis and thyroid disorders, in order to choose the most appropriate treatment.
When to get tested?
If you have an enlarged thyroid gland (goitre) and/or other thyroid tests (FT4, FT3 and TSH) indicate thyroid dysfunction; if there is clinical evidence suggesting thyroid disease; in some patients with related autoimmune diseases.
Sample required?
A blood sample taken from a vein in the arm.
What is being tested?
These tests look for the presence and amount of specific thyroid autoantibodies. These develop when a person’s immune system mistakenly recognises components of the thyroid as foreign (not “self”); they can cause chronic thyroiditis (inflammation of the thyroid), tissue damage and impaired thyroid function.
The thyroid is a small, butterfly-shaped gland lying flat against the windpipe. Its main hormones (thyroxine (T4) and triiodothyronine (T3)) are essential for regulating the rate of our metabolism. The body uses thyroid-stimulating hormone (TSH) to regulate the production of thyroid hormones and keep their level in the blood constant.
How is the sample collected for testing?
A blood sample taken from a vein in the arm (cubital vein).
1. How is it used?
2. When is it requested?
3. What does the result mean?
4. Is there anything else I should know?
1. How is it used?
Thyroid antibody testing is mainly requested to help diagnose an autoimmune thyroid condition and distinguish it from other forms of thyroiditis and thyroid disease. It can be used to investigate the cause of an enlarged thyroid gland (goitre) and/or as a follow-up when other thyroid test results (T3, T4 and/or TSH) show signs of thyroid dysfunction.
Thyroid antibody testing may also be requested if a person with an autoimmune condition not related to the thyroid, such as systemic lupus erythematosus, rheumatoid arthritis or pernicious anaemia, develops symptoms suggesting thyroid involvement. This involvement can occur at any time during the course of the other condition.
2. When is it requested?
Thyroid peroxidase antibodies: TPOAb
Autoimmune thyroid disease:
Hashimoto’s thyroiditis (95%); primary myxoedema (90%); Graves’ disease (18%)
When a patient has symptoms, or when test results suggest hypothyroidism;
when the doctor is considering starting treatment with lithium, amiodarone, interferon alfa or interleukin-2, medicines with a high risk of causing hypothyroidism in people with TPOAb
Thyroglobulin antibodies: TgAb
Used to monitor treatment for thyroid cancer. Also present in autoimmune thyroid diseases.
Not as reliable as TPOAb for screening for autoimmune thyroid disease. Thyroglobulin antibodies are measured together with thyroglobulin levels at regular intervals after treatment for thyroid cancer. The presence of thyroglobulin antibodies can interfere with the thyroglobulin test, which is used as a tumour marker.
TSH receptor antibodies
TRAb
Graves’ disease
When a patient has symptoms of hyperthyroidism; to monitor the effectiveness of treatment.
If a pregnant woman has an autoimmune thyroid disease (such as Hashimoto’s thyroiditis or Graves’ disease) or another autoimmune disorder and thyroid involvement is suspected, one or more thyroid antibodies may be measured at the beginning and end of the pregnancy. These tests help the doctor determine whether the baby may be at risk of thyroid dysfunction due to antithyroid antibodies, which can cross the placenta and cause hypothyroidism or hyperthyroidism in the foetus or newborn baby.
Thyroid antibody testing may also be used when a patient has reproductive difficulties that the doctor suspects are caused by autoantibodies.
3. What does the result mean?
Moderately raised levels of antithyroid antibodies can be found in a variety of thyroid diseases, such as colloid goitre, and temporarily in De Quervain’s thyroiditis.
Thyroid cancer is a very rare tumour in which low levels of antithyroid antibodies may be found.
Significantly raised concentrations generally indicate autoimmune thyroid disease such as Hashimoto’s thyroiditis, primary myxoedema and Graves’ disease. In general, the higher the level of antithyroid antibodies, the more likely it is that an autoimmune thyroid disease is present. If present in the mother, these antibodies can increase the risk of hypothyroidism or hyperthyroidism in the foetus or newborn baby.
Thyroid antibodies can also be associated with other autoimmune diseases, such as type 1 diabetes mellitus, pernicious anaemia, rheumatoid arthritis and systemic lupus erythematosus.
A certain percentage of people in good health may test positive for one or more antithyroid antibodies. Their prevalence tends to be higher in women and to increase with age. A person with no apparent thyroid problems who develops antithyroid antibodies will have their thyroid function monitored (T3, T4, TSH). Although in most cases thyroid dysfunction will never develop, some people may develop it after some time.
Monitoring thyroid cancer
Thyroglobulin antibody and thyroglobulin testing can be used to monitor some types of thyroid cancer. For technical reasons, thyroglobulin antibodies can sometimes interfere with the results of the thyroglobulin test. When monitoring thyroid cancer, if thyroglobulin or thyroglobulin antibody levels are high, or fall only slightly and then rise again over time, it may mean that treatment has not been effective and that the problem persists or has come back. If levels are falling or have dropped to low or undetectable levels, the treatment has probably been effective.
4. Is there anything else I should know?
The sensitivity and specificity of thyroid antibody tests are improving, but are not yet at the levels doctors would like. All thyroid antibody tests have changed over time, which is one of the reasons they have had so many different names. There is a variety of analytical methods, each differing in what it measures and in its reference range.
If tests are repeated over time (for monitoring), it is important that they are carried out with the same method and therefore in the same laboratory.
1. What can be done to prevent, reduce or remove thyroid antibodies?
2. Are thyroid antibodies part of routine testing?
1. What can be done to prevent, reduce or remove thyroid antibodies?
There are no lifestyle changes that can prevent or eliminate antithyroid antibodies. It is important that patients and doctors are aware of their presence so that appropriate clinical decisions can be made.
2. Are thyroid antibodies part of routine testing?
No, they are usually requested only when a patient has an enlarged thyroid or symptoms suggesting thyroid dysfunction. Routine thyroid screening is usually done with thyroid function tests such as TSH and fT4.