Autoantibodies to thyroid peroxidase in the blood

The reference values (norm) of the concentration of autoantibodies to thyroid peroxidase in serum are 0-18 IU / ml.

Thyroid peroxidase is an enzyme firmly 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. During further oxidation with peroxidase, mono- and diiodotyrosines are conjugated to form various iodothyronines, of which tetraiodothyronine (T ₄ ) predominates . It has now been established that antibodies to the antigens of the microsomal fraction are antibodies to 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 antibodies in the blood is always increased with thyroiditis Hashimoto, Graves' disease and idiopathic myxedema.

With thyroiditis Hashimoto as a result of destruction by autoantibodies thyroid peroxidase in the thyroid follicles, iodine metabolism is violated, which leads to its low content in thyroglobulin. Function of the thyroid gland is reduced mainly by reducing the secretion of T ₄.

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, antibodies to thyroid peroxidase more than 18 IU / ml are detected in 98 and 83% of cases, respectively. Specificity of this border for these diseases is 98%. Typically, the concentration of antibodies to thyroid peroxidase in the blood in patients with thyroiditis Hashimoto and Graves' disease is 100 IU / ml and above.

In connection with the fact that patients with autoimmune thyroiditis may have elevated levels of antibodies to thyroid peroxidase and / or thyroglobulin, it is advisable to determine them in a complex to improve the reliability of laboratory diagnostics.

Increase in the concentration of antibodies 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.

• antibodies to thyroglobulin.
  • Absolute indications: monitoring of post-operative treatment of thyroid cancer is mandatory in conjunction with the study of thyroglobulin (to exclude a 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.
• antibodies to thyroid peroxidase.
  • Absolute indications: diagnosis of Graves' disease, autoimmune thyroiditis in primary hypothyroidism, prognosis of hypothyroidism with isolated TSH increase, prognosis of postpartum thyroiditis in women of high risk group.
  • Relative indications: differential diagnosis of autoimmune (lymphocytic) and subacute thyroiditis in transient thyrotoxicosis, diagnosis of autoimmune thyroiditis in euthyroid diffuse or nodal goiter, prognosis of hypothyroidism in individuals in high-risk groups. Repeated (during treatment) study of the level of antithyroid antibodies in patients with established autoimmune thyroiditis is not advisable, since they have no prognostic significance. Patients with probabilistic autoimmune thyroid disease in the absence of antibodies in the blood during a primary examination are shown to re-define them during the first and second years of follow-up.

[1], [2], [3]