At a Glance
Why Get Tested?
To help diagnose and monitor autoimmune thyroid diseases and to distinguish these from other forms of thyroiditis, and thyroid disease; to help guide treatment decisions
When to Get Tested?
If you have an enlarged thyroid gland (goitre) and/or if your other thyroid tests (such as Free T3, Free T4, and TSH) indicate thyroid dysfunction; if there are clinical features to suggest thyroid disease; in some patients with related autoimmune diseases
Sample Required?
A blood sample taken from a vein in your arm
The Test Sample
What is being tested?
These tests detect the presence and measure the quantity of specific thyroid autoantibodies. These develop when a person’s immune system mistakenly recognizes components of the thyroid as foreign (not-self) and can lead to chronic thyroiditis (inflammation of the thyroid), 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 (thyroxine (T4) and triiodothyronine (T3)) are vital in helping to regulate the rate at which we use energy. The body has a feedback system that utilises thyroid stimulating hormone (TSH) to help turn thyroid hormone production on and off and maintain a stable amount of the thyroid hormones in the bloodstream. When thyroid antibodies interfere with this process, it can lead to chronic conditions and disorders associated with hypothyroidism (not enough thyroid hormones) or hyperthyroidism (excessive amounts of thyroid hormones). Hypothyroidism can cause symptoms such as weight gain, fatigue, goitre (enlarged thyroid gland), dry skin, hair loss, intolerance to cold, and constipation. Hyperthyroidism can cause symptoms such as sweating, rapid heart rate, anxiety, tremors, fatigue, difficulty sleeping, sudden weight loss, and protruding eyes.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
Thyroid antibody testing is primarily requested to help diagnose an autoimmune thyroid disease and to separate it from other forms of thyroiditis and thyroid disease. It 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 T3, T4, and/or TSH) show signs of thyroid dysfunction.
Thyroid antibody tests may also be requested if a person with a known non-thyroid-related autoimmune condition, such as systemic lupus erythematosus, 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).
When is it requested?
| Thyroid Antibody | Acronym | Present in | When ordered | |
|---|---|---|---|---|
| Thyroid peroxidase antibody |
TPOAb | Autoimmune thyroid disease: Hashimoto’s thyroiditis (95%); primary myxoedema (90%); Graves’ disease (18%) |
When patient has symptoms or test results suggesting hypothyroidism; when doctor is considering starting a patient on a drug therapy, such as lithium, amiodarone, interferon alspha, 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 |
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 fetus or newborn.
Thyroid antibody testing may also be used when a patient has reproductive difficulties that the doctor suspects may be associated with autoantibodies.
What does the test result mean?
Mild to moderately elevated levels of thyroid antibodies may be found in a variety of thyroid diseases, such as colloidal thyroiditis, and transiently in DeQuervain's thyroiditis.
Thyroid cancer is a very rare tumour, and low level thyroid antibodies can sometimes be detected.
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 fetus 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. Their prevalence tends to be higher in women and tends to increase with age. If a person with no apparent thyroid dysfunction has a thyroid antibody, her doctor will track her health over time, and monitor thyroid function tests (T3, T4, TSH). While most may never experience thyroid dysfunction, a few 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. 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.
Is there anything else I should know?
The sensitivity and specificity of thyroid antibody testing is improving but is still not as good as doctors would like it to be. All of the thyroid antibody tests have changed over time. This is part of the reason that they have gone by so many names. There are a variety of different methods and each of them can be a little different in what it is measures and what is the reference range.
If you are having serial testing done (for monitoring purposes), it is important to have testing done by the same laboratory with the same method.
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
