促甲状腺素受体抗体高是怎么回事
最佳答案：
THYROID AUTOANTIBODIES
# Overview
Thyroid autoantibodies are circulating antibodies against several thyroid antigens,which are present in most patients with autoimmune thyroid disorders,such as Hashimoto’s thyroiditis and Graves’ disease. The thyroid autoantibodies discussed here are widely available in clinical diagnostic laboratories and commonly used,and these include antibodies to thyroid peroxidase (TPOAb),antibodies to Tg (TgAb) and antibodies directed against the TSH receptor (TRAb).
# Available Assays
Modern assays for thyroid autoantibodies depend on direct measurement of the interaction between the autoantibody (patient’s serum) and the labeled thyroid antigen. Despite improvement of these assays in recent years,specificity remains an issue,because many euthyroid individuals exhibit low levels of these autoantibodies. The higher the concentration of the autoantibody,the greater is its clinical specificity. Attempts have been made to standardize these assays to allow for comparisons of thyroid autoantibody concentrations from one office visit to the next,among different patients,and among laboratories. However,owing to autoantibodies differing considerably in their affinity and epitope recognition of antigen,results from different commercial assays may still vary significantly.
# Clinical Usefulness and Test Interpretation
Autoantibodies to thyroid peroxidase and to thyroglobulin
Both TPO and Tg autoantibodies are polyclonal antibodies and are thought to occur owing to a secondary response to thyroid injury,and may contribute to the development and chronicity of disease. Almost 100% of patients with Hashimoto’s thyroiditis have elevated TgAb and TPOAb,but TPOAb have higher affinity and occur in higher concentrations. TgAb and TPOAb are also detectable in 50% to 90% of patients with Graves’ disease. These antibodies are also frequently seen in the general population and are 5-fold more common in women than in men. However,their significance in individuals with normal thyroid function remains uncertain,except that they confer a risk factor in families with autoimmune thyroid disorders.
In patients with known overt hypothyroidism,measurement of these antibodies is not required,because it does not alter management. However,current guidelines recommend measurement of TPOAb when evaluating patients with subclinical hypothyroidism,because their presence may influence the decision to treat. If positive,progression to overt hypothyroidism occurs at a rate of 4.3% per year versus 2.6% per year when TPOAb are negative. Additionally,measurement of TPOAb should be considered when evaluating patients with recurrent miscarriage,with or without infertility. This is because women with positive TPOAb may have an increased risk of miscarriage in the first trimester,for preterm delivery,and for offspring with impaired cognitive development. It is hypothesized that these increased risks may be owing to decreased thyroid functional reserve from chronic autoimmune thyroiditis leading to subtle hypothyroidism.
Autoantibodies to the thyroid-stimulating hormone receptor
TRAb are directed against the TSH receptor. In hyperthyroid patients with Graves’ disease,these autoantibodies behave as thyroid-stimulating antibodies (thyroid-stimulating immunoglobulin),because they compete with TSH for binding to its specific receptor site in the cell membrane. This stimulation induces thyroid growth,increases gland vascularity,and leads to an increased rate of thyroid hormone production and secretion. Other types of TRAbs exist,including antibodies that act as TSH antagonists and are referred to as blocking TRAbs (thyrotropin-binding inhibitor immunoglobulin) and neutral antibodies,which do not influence TSH binding but may act as weak agonists. Blocking TRAbs can be found in 15% of patients with autoimmune thyroiditis,especially in patients without a goiter. However,TRAbs are not detectable in the normal population with the use of currently available assays,and thus are disease specific.
Measurement of TRAbs can be used to diagnose Graves’ disease. Most TRAb assays are specific for Graves’ disease,but thyroid-stimulating immunoglobulin and first-generation thyrotropin-binding inhibitor immunoglobulin assays are less sensitive. – Measurement of TRAb levels before stopping antithyroid drug therapy is recommended,because it helps in predicting which patients can be weaned from the medication,with normal levels indicating a greater chance for remission. Persistently high levels of TRAb along with high thyroid blood flow identified by color Doppler ultrasound imaging are associated with higher relapse rates,– and these patients should be assessed more frequently and at shorter intervals after antithyroid drugs are discontinued. In contrast,patients with mild disease,small goiters,and negative TRAb have remission rates of greater than 50%,making the use of antithyroid medications potentially more favorable in this group of patients.
TRAb levels should be measured in pregnant women with hyperthyroidism when the etiology is unclear. If Graves’ disease is confirmed with elevated TRAbs,then these antibodies should be measured again at 22 to 26 weeks of gestation. In hypothyroid pregnant patients who were treated for Graves’ disease with radioactive iodine or thyroidectomy before pregnancy,TRAb levels should be measured using a sensitive assay either initially at 20 to 26 weeks of gestation,or initially during the first trimester,and if elevated,again at 22 to 26 weeks of gestation. This recommendation is based on the strong correlation between a high titer of TRAbs and the development of fetal or neonatal Graves’ disease,because TRAbs can cross the placenta and affect the fetal thyroid gland. Thus,TRAb levels measured at 22 to 26 weeks of gestation should be used to guide decisions regarding neonatal monitoring.","department":"
