Thyroid antibodies

What is being analysed?
This test detects the presence and measures the amount of specific thyroid autoantibodies. They appear when the immune system recognises thyroid components as foreign (non-self). They can cause chronic thyroiditis, tissue damage and impaired thyroid function.
A feedback system, via TSH, keeps the blood concentrations of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) stable. When thyroid antibodies interfere with this process, a chronic disorder can develop, with changes associated with hypothyroidism or hyperthyroidism.

How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?

How is it used?
Thyroid antibody testing is mainly requested to diagnose autoimmune thyroid disease and to distinguish it from other forms of thyroiditis.
It may be requested if the thyroid is enlarged (goitre) and/or other thyroid function tests (T3, T4 and TSH) indicate thyroid dysfunction.
One or more thyroid antibody tests may be requested if a patient with a known autoimmune condition not related to the thyroid, such as systemic lupus erythematosus, rheumatoid arthritis or pernicious anaemia, has symptoms suggesting thyroid involvement. During these conditions, thyroid involvement can occur at any time.

When is it requested?

In pregnancy, in the case of autoimmune thyroid disease (such as Hashimoto’s thyroiditis or Graves’ disease) or other autoimmune conditions with thyroid involvement, one or more thyroid antibodies may be measured in the first and last months.
These tests are used to assess the risk of thyroid disorders in the newborn baby, as the antibodies can cross the placenta and cause hypo- or hyperthyroidism in the foetus or newborn.

Thyroid antibody testing may be requested when there are symptoms of altered thyroid function in the presence of another autoimmune condition and/or in the case of reproductive difficulties suspected to be linked to autoantibodies.

What does the test result mean?
Mildly or moderately raised concentrations of antithyroid antibodies can be present in various thyroid and autoimmune conditions, such as thyroid cancer, type 1 diabetes, rheumatoid arthritis, pernicious anaemia and autoimmune collagen vascular diseases.
Significantly raised concentrations are found more often in autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease.
In general, their presence suggests autoimmune involvement of the thyroid, and the higher the concentrations, the more likely the disease. Progressively rising levels indicate an increase in autoimmune activity more significantly than stable levels do. If present in the mother, all these antibodies increase the risk of hypo- or hyperthyroidism in the foetus or newborn.
If thyroglobulin antibodies are present while thyroglobulin levels are being monitored, they can interfere with the test results, so thyroglobulin cannot be used as a thyroid tumour marker.
If the thyroglobulin antibodies used for monitoring stay high, or fall at first but then rise progressively, the treatment is probably not effective or the problem persists or has come back.
If concentrations fall to low or undetectable levels, the treatment is probably effective.
A certain percentage of healthy people may test positive for one or more thyroid antibodies. Their prevalence tends to be higher in women and to increase with age. The presence of antithyroid antibodies without apparent thyroid dysfunction should be followed over time. In most cases thyroid dysfunction will never develop, but a small percentage of people may develop it in the future.

Is there anything else I should know?
The sensitivity and specificity of thyroid antibody testing are improving but are not yet satisfactory from a clinical point of view. All the different laboratory tests for thyroid antibodies have changed over time, which partly explains the many different names. Numerous methods are available that measure slightly different parts of the molecule and therefore have different reference ranges. For monitoring, which involves periodic measurements, it is therefore important that the test is carried out in the same laboratory with the same method. Adding to the complexity of thyroid antibody testing is the fact that the antibodies are not uniform. Because the types of laboratory test developed so far “capture” different types and amounts of the antibodies present in the blood, their sensitivity varies and can sometimes differ significantly.

1. What can be done to prevent, reduce or eliminate thyroid antibodies?
2. Is thyroid antibody testing a routine test?

1. What can be done to prevent, reduce or eliminate thyroid antibodies?
Lifestyle changes or treatment cannot prevent or eliminate thyroid antibodies. It is important to monitor them to minimise their effects on thyroid function.

2. Is thyroid antibody testing a routine test?
No, they are usually requested when the thyroid is enlarged or there are symptoms suggesting thyroid dysfunction. Thyroid function is usually assessed by measuring TSH and T4.