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 (goiter) and/or performed as a follow-up when other thyroid test results (such as T3, T4, 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 anemia, develops symptoms that suggest thyroid involvement. This involvement may occur at any time during the course of the other condition(s).

Thyroid Antibody	Acronym	Present in:	When ordered:	Other Facts
Thyroid peroxidase antibody	TPOAb	Hashimoto’s thyroiditis; Graves’ disease	When patient has symptoms suggesting hypothyroidism; when doctor is considering starting a patient on a drug therapy, such as lithium, amiodarone, interferon alpha, or interleukin-2, that has associated risks of developing hypothyroidism when TPOAb are present	Has been associated with reproductive difficulties, such as miscarriage, pre-eclampsia, premature delivery, and in-vitro fertilization 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; since the thyroglobulin test will be ordered at regular intervals after thyroid cancer treatment, TgAb will also be ordered at regular intervals
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 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.

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 anemia, 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 the mother, can increase the risk of hypothyroidism or hyperthyroidism in the fetus 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 tumor 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. 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. While most may never experience thyroid dysfunction, a few may develop it in the future.

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.