At a glance

Also known as

Thyroid autoantibodies; antithyroid antibodies; antimicrosomal antibody; thyroid microsomal antibody; thyroperoxidase antibody; TPOAb; anti-TPO; antithyroglobulin antibody; TgAb; TSH receptor antibody

Why get tested?

To help diagnose and monitor autoimmune thyroid diseases and to distinguish these from other forms of thyroiditis; 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 FT3, FT4, and TSH) indicate thyroid dysfunction; along with a thyroglobulin test when your doctor is using it as a monitoring tool; at intervals recommended by your doctor when you have a known autoimmune thyroid disorder

Sample required?

A blood sample drawn from a vein in your arm

Test preparation needed?

None

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 recognises components of the thyroid as foreign (not-self), which 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 – metabolism. 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) such as Hashimto thyroiditis or hyperthyroidism (excessive amounts of thyroid hormones) seen in Graves' disease. 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

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

Thyroid antibody testing is primarily ordered to help diagnose an autoimmune thyroid disease and to separate it from other forms of thyroiditis. It may be ordered 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 FT3, FT4, and/or TSH) show signs of thyroid dysfunction.

One or more thyroid antibody tests may also be ordered 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: Other Facts
Thyroid peroxidase antibody TPOAb Hashimoto’s thyroiditis; Graves’ disease When a patient has symptoms suggesting thyroid disease; when a doctor is considering starting a patient on a drug therapy that has associated risk of developing thyroid dysfunction when TPOAb are present, (e.g. lithium, amiodarone, interferon alpha, or interleukin-2). Has been associated with reproductive difficulties, such as miscarriage, pre-eclampsia, premature delivery, and in-vitro fertilisation failure
Thyroglobulin antibody TgAb Thyroid cancer; Hashimoto’s thyroiditis Whenever a thyroglobulin test is performed to see if the antibody is present and likely to be interfering with the test results; at regular intervals after thyroid cancer treatment; when symptoms of hypothyroidism are present   
Thyroid stimulating hormone receptor antibody TRAb Graves’ disease When a 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 ordered 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 ordered when a patient with another autoimmune disorder has symptoms of thyroid dysfunction and/or when she has reproductive difficulties that the doctor suspects may be associated with autoantibodies.

What does the test result mean?

Negative test results means that autoantibodies are not present in the blood at the time of testing and may indicate that symptoms are due to a cause other than autoimmune thyroid disease.

Mild to moderately elevated levels of thyroid antibodies may be found in a variety of thyroid and autoimmune disorders, such as thyroid cancer, Type 1 diabetes, rheumatoid arthritis, pernicious anaemia, and autoimmune collagen vascular diseases. Significantly increased concentrations most frequently indicate thyroid autoimmune diseases such as Hashimoto’s thyroiditis and Graves’ disease.

In general, their presence suggests that there is autoimmune thyroid involvement and the higher the level, the more likely that is. Rising levels may be more significant than stable levels as they indicate an increase in autoimmune activity. All of these antibodies, if present in a pregnant woman, can increase the risk of hypothyroidism or hyperthyroidism in the developing baby or newborn.

If TgAb are present when the doctor is monitoring thyroglobulin levels, they will interfere with the test results. This may mean that the doctor will not be able to use thyroglobulin as a tumour marker for thyroid cancer. If TgAb is being used as a monitoring tool and has stayed high or dropped low initially but is increasing over time, then it is likely 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 is effective.

A certain percentage of patients who are healthy may be positive for one or more thyroid antibodies. The 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. While most may never experience thyroid dysfunction, a few may develop it in the future.

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 lot of different methodologies and each of them is a bit different in what it is measuring and in the normal ranges. If you are having serial testing done (for monitoring purposes), it is important to have testing done by the same laboratory with the same methodology. Adding to the complexity of thyroid antibody testing is the fact that the antibodies are not homogenous. The tests that have been developed pick up varying amounts of the antibody population in the blood, affecting their sensitivity.

Common Questions

What can be done to prevent, lower, or get rid of thyroid antibodies?

There are no lifestyle changes or therapies that can prevent or eliminate thyroid antibodies. It is important for patients and their doctors to be aware of them when they are present and to work to minimise their effect on thyroid function.

Are thyroid antibodies part of routine testing?

No, they are usually only indicated when a patient has an enlarged thyroid or symptoms suggesting thyroid dysfunction. Routine screening of the thyroid is usually accomplished using thyroid tests such as TSH and FT4.

Last Review Date: Feb 19, 2014