Thyroid peroxidase and antibodies to it: analysis, norm, reasons for the increase
The content of the article:
- Laboratory blood test for antibodies to thyroperoxidase
- Antibodies to thyroperoxidase are elevated: what does this mean?
- Treatment
Thyroid peroxidase (thyroid peroxidase, TPO) is a key enzyme in the biosynthesis of thyroid hormones.
Thyroid peroxidase is a type I glycosylated transmembrane protein produced in the thyroid gland. Its synthesis occurs on polyribosomes, glycosylation of the protein core of the molecule - in the endoplasmic reticulum, the maturation of the enzyme ends in the Golgi complex. A significant part of the enzyme is found on the perinuclear membrane, in the endoplasmic reticulum and intracellular vesicles. Ripe thyroid peroxidase is transported to the apical pole of thyrocytes.
Thyroid peroxidase - an enzyme actively involved in the synthesis of thyroid hormones
Thyroid peroxidase catalyzes the iodination of the tyrosine residues of thyroglobulin (a protein produced by the follicular cells of the thyroid gland) and the fusion of iodotyrosines during the synthesis of the hormones T 3 (triiodothyronine) and T 4 (thyroxine). Triiodothyronine and thyroxine, in turn, are of no small importance for the regulation of metabolism in the body.
For the reactions that are carried out by thyroid peroxidase, iodine, hydrogen peroxide and thyroglobulin are required. Reduction or complete absence of thyroid peroxidase activity refers to the causes of congenital hypothyroidism.
Thyroid peroxidase is one of the main antigens in autoimmune diseases of the thyroid gland. In such pathologies as Hashimoto's thyroiditis and Graves' disease (occurring with thyrotoxicosis), there is a loss of immunological tolerance to TPO. Specific markers of these diseases are antibodies to thyroperoxidase (AT-TPO, antibodies to the antigen of the microsomal fraction of thyrocytes).
Antibodies to thyroid peroxidase are produced mainly by B-lymphocytes, which infiltrate the thyroid gland, the level of antibodies reflects the severity of lymphoid infiltration. The prevalence of antibodies to TPO among persons without thyroid dysfunction is approximately 26%.
Laboratory blood test for antibodies to thyroperoxidase
Determination of antibodies to thyroperoxidase is the most accurate method for detecting autoimmune diseases of the thyroid gland, including in the early stages. Timely and correct diagnosis of 85% of cases of diffuse toxic goiter and 95% of cases of Hashimoto's thyroiditis is carried out thanks to a high-precision study for autoantibodies to thyroid peroxidase.
This analysis is included in the diagnostic complex for studying the functions of the thyroid gland along with the determination of the concentration of thyroid-stimulating hormone, total and free triiodothyronine and thyroxine, thyroglobulin, as well as antibodies to it.
Determination of the level of antibodies to TPO is carried out in women at risk during pregnancy, since antibodies are able to pass through the placental barrier and affect the development of the fetal thyroid gland.
If, after childbirth, a woman is diagnosed with thyroiditis, and antibodies to thyroid peroxidase are detected in the blood, a similar study is also prescribed to a newborn, this is done in order to exclude this pathology in children or to detect it early.
The analysis is also prescribed in order to identify the causes of pre-eclampsia in pregnant women, spontaneous abortion or premature birth, menstrual irregularities, infertility, and also before in vitro fertilization.
When treating with lithium or interferon preparations, an analysis is carried out for antibodies to thyroperoxidase, since these substances can cause the development of thyroid diseases in carriers of antibodies to TPO. The study is shown with prolonged use of hormonal drugs, it is repeated at regular intervals in order to monitor the effectiveness of the therapy.
Anti-thyroid peroxidase antibody levels are also checked if there are symptoms suggestive of impaired thyroid function, in particular, decreased (weight gain, constipation, chronic fatigue, dry skin, hair loss, increased sensitivity to cold) or increased (increased sweating, tachycardia, exophthalmos, unmotivated weight loss, sleep disturbances, anxiety) the level of thyroid hormones.
Blood for analysis for antibodies to thyroperoxidase is taken early in the morning on an empty stomach, it is only allowed to drink non-carbonated water. A month before the study, you need to stop taking hormonal drugs, a few days - iodine-containing drugs. The day before blood sampling, it is recommended to exclude physical and mental stress, as well as smoking. The study should not be carried out for some time after surgery or an infectious disease, as the result may be distorted.
The rates of antibodies to thyroid peroxidase depending on age are presented in the table:
| Age | Reference values, U / l |
| Under 50 | <35 |
| Over 50 years old | <100 |
In different laboratories, the rates of antibodies to thyroid peroxidase may differ. If it is necessary to control this indicator, it is recommended to do repeated analyzes in the same laboratory.
If antibodies to thyroid peroxidase are strongly elevated, additional studies (including ultrasound) are prescribed to detect or exclude thyroid pathologies.
Antibodies to thyroperoxidase are elevated: what does this mean?
Antibodies to thyroperoxidase are increased in systemic (autoimmune) diseases, which include rheumatoid arthritis, pernicious anemia, systemic lupus erythematosus, etc. A deviation from the norm of this indicator is observed in idiopathic hypothyroidism, adenoma or thyroid cancer.
If elevated bodies are detected for thyroperoxidase, an ultrasound of the thyroid gland is additionally performed
Antibodies to thyroid peroxidase can also increase in the absence of pathological processes, for example, in older women. In such cases, additional diagnostics are carried out and, as a rule, expectant tactics are chosen.
An increase in the level of antibodies to thyroid peroxidase during pregnancy can occur due to changes in the immune system, as well as the peculiarities of the functioning of the thyroid gland during this period. As a rule, 8-9 months after childbirth, the indicator returns to normal, treatment is not required. However, sometimes it is during pregnancy that diseases are detected, against which an increase in antibodies occurs. A high level of antibodies to thyroid peroxidase in women during pregnancy can cause hyperthyroidism in an unborn child.
Reasons for a moderate increase in antibodies to thyroperoxidase:
- hereditary predisposition;
- exogenous factors (injury to the thyroid gland, exposure to the body of toxic substances or ionizing radiation, etc.);
- some pathologies of the thyroid gland;
- B 12 - deficiency anemia;
- type 1 diabetes mellitus;
- transferred or chronic infectious diseases;
- taking drugs with a high iodine content;
- long-term irrational use of medicines.
A gradual increase in the indicator usually indicates the progression of the pathological process.
A significant increase in antibodies to thyroid peroxidase is noted in autoimmune thyroiditis (values may exceed 1000 U / L).
At the initial stage of the development of pathologies characterized by an excess of antibodies to TPO, any pronounced manifestations are often absent. At advanced stages, patients complain of weakness, fatigue, apathy or, on the contrary, irritability, their nails, hair, skin condition worsens, there is swelling of the face, trunk and lower extremities. The general condition and cognitive abilities deteriorate, the level of blood pressure and body temperature can be lowered, dysfunctions of the gastrointestinal tract, cardiovascular, nervous, and reproductive systems develop. The thyroid gland is often enlarged in order to compensate for the lack of hormones, which leads to pain when swallowing and hoarseness of the voice.
Treatment
Before treating a patient with an elevated level of antibodies to thyroperoxidase, the exact cause of the pathology should be established.
Treatment with elevated antibodies to thyroperoxidase against the background of autoimmune thyroid diseases is aimed at eliminating thyrotoxicosis. For this purpose, drug therapy (taking thyreostatic drugs), surgical treatment (thyroidectomy) or treatment with radioactive iodine (radioiodine therapy) is carried out.
The main indications for resection of the thyroid gland include the ineffectiveness of conservative therapy, development of cardiovascular complications against the background of thyrotoxicosis, and neoplasms of the thyroid gland.
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Anna Aksenova Medical journalist About the author
Education: 2004-2007 "First Kiev Medical College" specialty "Laboratory Diagnostics".
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