The antibodies to TSH receptors, also known as anti TSH, anti rTSH, anti TSHR, TrAb or TSH ab, they are auto antibodies to the receptor that binds thyrotropin (TSH). They are very common in autoimmune thyroid diseases such as Graves' disease, and are divided into stimulated antibodies and TSH receptor inhibiting antibodies.
TSH receptor antibodies normal values
They are considerate normal negative TSH receptor antibody values, i.e. less than 1.0 IU / L, where “UI” stands for international units.
They are considerate tall positive TSH receptor antibody values, i.e. higher than 1.5 IU / L.
There is a "gray" area in which it will not be possible to establish with certainty the positivity or negativity of TSH receptor antibodies: the doubtful result is positioned between values between 1.0 UI / L and 1.5 UI / l.
Anti-thyroid antibodies, more correctly defined as thyroid auto-antibodies, are antibodies which, instead of attacking antigens (parts) of organisms foreign to our body, attack components of the gland thyroid. They are produced when our immune system reacts against certain components of the thyroid, causing chronic inflammation of the gland (called thyroiditis), which causes damage to the thyroid tissues to the point of compromising their functionality.
There thyroid it is a small, butterfly-shaped gland located close to the trachea, in the anterior region of our neck. The thyroid, stimulated by TSH (thyroid stimulating hormone or thyroid stimulating hormone), produces thyroid hormones, namely T3 (triiodothyronine) and (T4) thyroxine, which are essential for an adequate use of energy and a balanced metabolism of our body.
In the presence of anti-thyroid antibodies, the gland can be damaged in some of its components, and consequently autoimmune diseases can arise with associated thyroid malfunction, which can be characterized both by an increased function, that is by hyperthyroidism, both from a glandular hypofunction, or from hypothyroidism.
Follow the official page of Exams and Values! If you haven't already, sign up for Google+ and click "Follow".
The most commonly researched anti-thyroid antibodies are:
- antibodies to thyroglobulin (anti Tg): they are auto antibodies directed against thyroglobulin, which is a precursor of the thyroid hormones, thyroxine and triiodothyronine.
- Thyroid peroxidase antibodies (anti TPO): they are auto antibodies directed against thyroid peroxidase, an enzyme responsible for the formation of thyroid hormones starting from iodine.
- Antibodies to TSH receptors (anti rTSH): they are antibodies that bind to the receptor present in the thyroid cells that normally binds TSH. They are distinguished in TSH receptor stimulating antibodies and TSH receptor inhibiting antibodies.
TSH receptor antibodies: what they are
The thyrotropin receptor (TSH) is a glycoprotein consisting of 398 amino acids. Its function is to bind the TSH hormone, which is produced by the pituitary gland, and which is the main regulator of the function of the thyroid gland.
In fact, TSH is synthesized by the pituitary in response to the positive stimulus of TRH, a hormone produced by the hypothalamus in the presence of low levels of thyroid hormones. In other words, when there are not enough thyroxine (T4) and triiodothyronine (T3), the two thyroid hormones in our body, TRH stimulates the production of TSH, which in turn acts on the thyroid receptors, to "control ”The production of other thyroid hormones that bring the values back to the normal range.
Obviously, the presence of antibodies that bind to the TSH receptor, will interfere with this mechanism, called the hypothalamic-pituitary-thyroid axis.
If the antibody will act blocking the thyrotropin receptor, we will talk about TSH receptor blocking antibodies (TBAb), if instead the antibodies in some way act by stimulating the receptor for the thyroid stimulating hormone, we will talk about TSH-stimulating antibodies (TSAb).
There are also antibodies to TSH receptor neutral, that is, which do not activate or inhibit the receptor present on the surface of thyroid cells: in the presence of these auto antibodies there will be no effect on thyroid function.
Help make this article more visible: click on +1!
TSH receptor antibodies: when to perform the analysis
The search for antibodies against the TSH receptor is generally required:
- To have a biohumoral confirmation of the clinical diagnosis of Graves' disease. This pathology, as we will see later, should be suspected if the typical symptoms of hyperthyroidism are present.
- For a better evaluation in case of exophthalmos ("protruding" eye), even in conditions of euthyroidism.
- To evaluate the risk of thyrotoxicosis in the newborn due to placental transmission of maternal antibodies during pregnancy.
- As a prognostic marker of relapse (relapse) in patients with Graves' disease, 4-8 months after the end of drug therapy.
TSH receptor stimulating antibodies
If the TSH receptor antibodies are of the stimulating type, the activation of an enzyme (adenylate cyclase) will lead to the production of a greater quantity of thyroid hormones, with the consequent development of hyperthyroidism. This type of antibody is called TSI (Thyroid Stimulating Immunoglobulins) and they are IgG type immunoglobulins.
Causes of TSH receptor-stimulating antibodies positive
Antibodies to thyrotropin receptor are found in the following pathologies:
Graves-Basedow disease: is an autoimmune thyroid disease, the most common of those causing hyperthyroidism. It is characterized by the classic symptoms of hyperthyroidism: anxiety, restlessness, tremors, diarrhea, weight loss, tachycardia and palpitations. Stimulant-type TSH receptor antibodies are positive in 70-100% of cases.
These autoantibodies also appear to play a key role inophthalmopathy in the course of Graves' disease: it is believed that they bind to the raceptors for TSH present in the retro-orbital tissue (behind the eyeball), causing an inflammatory state with activation of the lymphocyte system and production of pro-inflammatory cytokines: at this it follows the activation of particular cells, the fibroblasts, which produce tissue that goes to deposit behind the ocular orbit "pushing" the eye outwards.
Myxedema: accumulation of mucopolysaccharide tissue and fluid at the subcutaneous level that occurs in severe hypothyroidism (Hashimoto's thyroiditis), but also, with the same mechanism as ophthalmopathy, also in hyperthyroidism due to Graves' disease. Also in this condition, altered values of TRAb can be found.
Other autoimmune conditions: as for other thyroid autoantibodies, there are autoimmune pathologies characterized by the presence of antibodies even in the absence of thyroid pathologies. We recall among these: pernicious anemia, autoimmune gastritis, type 1 diabetes mellitus, myasthenia gravis, alopecia, pheochromocytoma, Addison's disease, rheumatoid arthritis, systemic lupus erythematosus (SLE), Sjogren's syndrome.
Thyroid stimulating hormone receptor antibodies can also be used for monitoring thyroid ablative therapy. For example, if a thyroid therapy is started in the course of Basedow-Graves' disease (that is, it puts the thyroid to "rest"), and the anti-TSH receptor antibodies, checked after 12-18 months, are low titre or negative , one can imagine a response to therapy. If, on the other hand, they remain high or return to highs after a period of relative normalization, we will speak of persistence or recurrence of the disease.
TSH receptor inhibiting antibodies
The other side of the coin is antibodies inhibitors the TSH receptor. This type of auto antibody occupies the receptor without activating any cascade of signals stimulating the production of thyroid hormones, but rather preventing thyrotropin from binding. They are also called TBII (Thyrotropin-Binding Inhibiting Immunoglobulins), and they are an immunoglobulin of the IgG class.
Causes of antibodies inhibiting TSH positive receptors
This type of antibody is often found in Hashimoto's thyroiditis, in the company of another type of autoantibody, anti-TPO (Thyroid Thyroid Peroxidase).
Antibodies to TSH receptor with inhibiting action can also often be found in those patients with Graves' disease who, after a few months / years of hyperthyroidism, slowly slide towards a state of hypothyroidism, or in those patients with a fluctuating course, which alternate phases of hypertoriodism with phases of euthyroidism (ie of normal thyroid function). It is hypothesized that those responsible for these mechanisms are the presence of antibodies blocking the thyrotropic hormone receptor.
Factors that can alter the measurement
The administration of radioactive iodine in the week preceding the examination can alter the result. Furthermore, as already mentioned, during the thyreostatic treatment the values of anti-TSH receptor antibodies in the blood can decrease.
Help make this article more visible: click on +1!Tags: Laboratory medicine Blood