Autoantibodies to thyroid peroxidase in serum
Reference values of the concentration of autoantibodies to thyroid peroxidase in serum - 0-18 IU / ml.
Thyroid peroxidase is an enzyme strongly bound to the granular endoplasmic reticulum of epithelial cells of the thyroid follicles. It carries out the oxidation of iodides in the follicles to active iodine and iodination of tyrosine. In the course of further oxidation with peroxidase, mono- and diiodotyrosines are conjugated to form various iodothyronines, of which tetraiodothyronine( T4) has a quantitative ratio of
.At present, it has been established that the AT to the Arg of the microsomal fraction is also an AT to the thyroid peroxidase.
Determination of the concentration of autoantibodies to thyroid peroxidase is used as a marker of thyroid diseases caused by autoimmune processes. The concentration of AT in the blood is always increased with thyroiditis, Hashimoto, Graves' disease and idiopathic myxedema.
In thyroiditis Hashimoto as a result of destruction of autoantibodies of thyroid reperoxide oxidase in the follicles of the thyroid gland, iodine metabolism is disrupted, which leads to its low content in thyroglobulin. Function of the thyroid gland is reduced mainly due to a decrease in secretion of T4.
When evaluating the results of the study, it is necessary to take into account the so-called "borderline" line, which is 18 IU / ml and is used to differentiate patients with euthyroid status and patients with Hashimoto's thyroiditis and Graves' disease. In patients with thyroiditis Hashimoto and Graves' disease, the content of AT to thyroid peroxide oxidase more than 18 IU / ml is revealed in 98 and 83% of cases, respectively. Specificity of this border for these diseases is 98%.Typically, the concentration of AT to thyroid peroxidase in the blood in patients with thyroiditis Hashimoto and Graves' disease is 100 IU / ml and above.
Due to the fact that in patients with autoimmune thyroiditis the level of AT to thyroid peroxidase and / or thyroglobulin may be increased, it is expedient to determine them in a complex to improve the reliability of laboratory diagnostics.
Increase in the concentration of AT to thyroid peroxidase in the blood can be detected with thyroiditis Ridel, Addison's disease.
Clinical indications for the study of antithyroid antibodies are as follows.
■ AT to thyroglobulin.
□ Absolute indications: monitoring of post-operative treatment of thyroid cancer necessarily in combination with thyroglobulin( to avoid false negative result);at a thyroglobulin concentration in the serum above 2.5-3 μg / l in patients who have suffered extirpation of the thyroid gland, it is necessary to exclude the presence of metastases and / or relapse of cancer.
■ AT to thyroid peroxidase.
□ Absolute indications: diagnosis of Graves' disease, autoimmune thyroiditis in primary hypothyroidism, hypothyroidism risk forecast with isolated TSH increase, prognosis of postpartum thyroiditis in high-risk women.
□ Relative indications: differential diagnosis of autoimmune( lymphocytic) and subacute thyroiditis with transient thyrotoxicosis, diagnosis of autoimmune thyroiditis in euthyroid diffuse or nodal goiter, prognosis of hypothyroidism in individuals in high-risk groups.
Repeated( in the process of treatment) study of the level of antithyroid antibodies in patients with established autoimmune thyroiditis to conduct is inexpedient, since they have no prognostic significance. Patients with probabilistic autoimmune thyroid disease
in the absence of AT in the blood during a primary examination are shown to re-define them during the first and second years of follow-up.