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).
|Thyroid peroxidase antibody
||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, , premature delivery, and in-vitro fertilisation failure
||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
||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.
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.
The and 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.