In recent years, the incidence of thyroid disease has been increasing year by year, among which autoimmune thyroid disease (AITD) has a prevalence of about 10% in the population.
The incidence of autoimmune thyroid disease (AITD) is about 10% in the population, and some retrospective studies have even pointed out that autoimmune thyroid disease may be related to the development of thyroid cancer, so more and more medical practitioners are focusing on the diagnosis and treatment of this disease.
Changes in thyroid hormone levels in the blood signify changes in thyroid function, so the convenient and easy to perform thyroid function test has become the choice of the majority of endocrinologists. Nowadays, a complete thyroid function report contains not only thyroid hormone indicators, but also various humoral immune indicators such as TRAb, TgAb, TPOAb, etc. Such hormones as T3, T4 and TSH are easy to read and treat, but what about the remaining antibodies? What do they mean? And is it necessary to keep them at normal values?
What are TRAb, TgAb and TPOAb?
TRAb, or TSH receptor antibody, is a member of the G-protein-coupled receptor superfamily, whose antigen is the TSH receptor on thyroid cells, and can be broadly classified as TSH receptor stimulating antibody (TSAb), TSH stimulation blocking antibody (TSBAb) and TSH receptor binding inhibitory immunoglobulin (TBII). In the presence of hyperthyroidism, TRAb is defined as TBII. they bind to TSH receptors on thyroid cells, causing thyroid hyperplasia and excessive or excessive thyroid hormone production, and are considered to be one of the important factors causing autoimmune thyroid disease.
TgAb, thyroglobulin antibody, is the earliest autoantibody found in the thyroid gland. Its main antigen is thyroglobulin in the follicular gel of the thyroid gland, which has a cytotoxic effect and can cause excessive destruction of thyroid epithelial cells and produce hypothyroidism, but the titer of this antibody does not correlate significantly with the degree of thyroid disease and may only be TPOAb, thyroid peroxidase antibody, formerly known as thyroid microsomal antibody (AMA), is an antibody induced by microsomal antigen from the cytoplasm of thyroid epithelial cells and has antibody-dependent cell-mediated cytotoxic and complement-dependent cytotoxic effects. It can maintain and aggravate thyroid damage, but does not have the effect of causing thyroid immune damage.
Why do these indicators keep fluctuating?
Before we can clarify the significance of antibody indicators, we must first clarify another issue: test results from different hospitals or laboratories cannot be viewed as equivalent!
With the advancement of testing technology, the sensitivity and accuracy of antibody testing has improved qualitatively. Although a unified international reference standard has been used, there is still a large variability in the indicators due to the different testing methods and reagents used by each laboratory, so different laboratories must establish their own unique standard of normal values, and if the brand and model of reagents are changed, the reference values also need to be re If the brand and type of reagents are changed, the reference values need to be adjusted again.
Therefore, if thyroid antibodies are measured in different hospitals, the comparability of the results will be reduced, and it is only possible to conclude whether the test results are within normal values or not, and not to conclude whether the condition has improved or worsened by simply comparing the values.
What diseases are indicated by abnormalities in these antibody indicators?
TRAb, especially TSAb, is mainly used for the diagnosis, identification and late prognosis of Graves’ disease. Since some patients with Graves’ disease will have a negative TRAb, the TRAb value cannot be used as the only diagnostic criterion for Graves’ disease. Instead, a negative TRAb can generally identify Graves’ disease in other thyrotoxic conditions such as subacute thyroiditis, painless thyroiditis, postpartum thyroiditis and toxic nodular thyroiditis.
Also, TRAb can be used as a predictor of Graves’ disease. The specificity and sensitivity of using TRAb values to predict recurrence of Graves’ disease after treatment is above 50%, but since the current test results indicate the percentage of TSH receptor activation or inhibition, the results are affected by changes in the ratio of TRAb to TSBAb and still need to be treated with caution.
In terms of Graves’ ophthalmopathy, TRAb can provide some discrimination between unilateral proptosis and proptosis with normal thyroid function, and can also predict the risk of developing Graves’ ophthalmopathy after radioiodine treatment in patients with Graves’ disease.
Since TRAb can pass through the maternal placenta, if a woman has Graves’ disease or hypothyroidism during pregnancy, TSAb and TSBAb can pass through the placenta into the newborn, causing hyper- or hypothyroidism in the newborn and affecting the neurological development of the child. Therefore, a woman should have her body tested for TRAb before pregnancy. If the test result confirms a positive TRAb, treatment should be given to normalize the TRAb level before pregnancy.
TgAb is a hallmark antibody of autoimmune thyroid disease, mostly appearing at the same time as TPOAb, with a higher positive rate in women than in men, and gradually increasing with age. In areas with endemic goiter, patients should be monitored for TgAb levels when treated with iodine supplementation because iodine increases the immunogenicity of Tg, especially in an already damaged thyroid gland, causing simple goiter to develop into autoimmune thyroid disease and making treatment more difficult.
In addition, TgAb has an important role as an adjuvant for monitoring thyroid cancer. tg is important in the prognosis and intraoperative monitoring of patients with well-differentiated thyroid cancer, but because the test results are susceptible to serum TgAb, the TgAb concentration needs to be tested before testing for Tg. In contrast, continuous monitoring of TgAb levels can replace Tg as an independent tumor surveillance index in patients with differentiated thyroid cancer. Normally, the TgAb level in patients with differentiated thyroid cancer will gradually decrease after radical surgery and turn negative within 1-4 years. If the TgAb level increases again, it can be the first indication of tumor recurrence.
TPOAb is also the hallmark antibody of autoimmune thyroid disease. Its level reflects the degree of lymphocyte infiltration and is highly positive in Hashimoto’s thyroiditis, Graves’ disease and postpartum thyroiditis, as well as in the general population. It was found that the positive rate of TPOAb was significantly higher in patients with other non-thyroidal autoimmune diseases such as type 1 diabetes, pernicious anemia, and in immediate family members with autoimmune thyroid disease, suggesting the potential for impairment of thyroid function in patients.
TPOAb is the gold standard for the diagnosis of Hashimoto’s thyroiditis, and its sensitivity and accuracy is even better than that of fine needle aspiration of the thyroid gland. A positive TPOAb is sufficient to confirm the diagnosis of autoimmune thyroid disease.
TPOAb can also be used as an adjunct to the diagnosis of Graves’ disease, especially in the diagnosis of patients who are negative for TRAb as mentioned earlier. Also, extremely high TPOAb titers in patients with Graves’ disease suggest that the patient may also have Hashimoto’s thyroiditis, and in such patients, treatment should be sensitive to the patient’s risk of developing spontaneous hypothyroidism.
In early pregnancy, a positive maternal TPOAb often indicates the possibility of maternal thyroiditis in the postpartum period. It has also been suggested that a positive TPOAb in early pregnancy with subclinical hypothyroidism or hypothyroid hormoneemia can impair early fetal neurological development and cause reduced intelligence.
Summary
Testing for thyroid autoantibodies is important for the diagnosis and identification of autoimmune thyroid disease, but each laboratory should establish its own unique normal reference values; TRAb is mainly used for the diagnosis of Graves’ disease, TPOAb for the diagnosis of Hashimoto’s thyroiditis, and TgAb as an adjunctive diagnostic criterion for thyroid cancer. All pregnant women should be tested for thyroid function and autoantibodies to reduce damage to the fetal nervous system and to ensure the quality of childbirth.