Content
Introduction
Antibodies are molecules produced by the body's defense system (immune system) to fight foreign elements, such as viruses and bacteria. Sometimes the immune system can, by mistake, make antibodies against elements of its own body.
Thyroid peroxidase (TPO) is an enzyme (molecule capable of accelerating and facilitating chemical reactions) present in thyroid cells and plays an important role in the production of thyroid hormones such as thyroxine (T4) and triiodothyronine (T3).
Thyroid peroxidase antibodies (anti-TPO) are antibodies produced by the immune system which, by mistake, attack this enzyme.
The presence of anti-thyroid peroxidase antibodies therefore indicates an autoimmune disease of the thyroid gland.
In particular, if the values are high, the presence of diseases such as:
- Hashimoto's thyroiditis
- Graves' disease
- idiopathic myxedema of the adult
An increase in anti-thyroid peroxidase antibodies can also be found in other autoimmune diseases. When it appears during the first trimester of pregnancy it can indicate an increased risk of postpartum thyroiditis.
Low anti-TPO values may also be present in healthy people with no signs of disease and are more frequent in women and with increasing age.
The test
The test for the assay of anti-thyroid peroxidase antibodies (whose abbreviations can be: Anti-TPO or TPOA) is the most important test for recognizing autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease. This test is usually associated with the search for antibodies to thyroglobulin (ATG), ie antibodies that attack thyroglobulin, a molecule produced by the thyroid, and are part of the group of thyroid autoantibodies.
The test consists of a simple blood sample from a vein in the arm. In the previous 12 hours it is recommended to fast and avoid taking multivitamins or supplements that contain biotin (a substance that is used to strengthen nails or hair) because it could alter the result.
Results
The anti-peroxidase antibody test is mainly prescribed to investigate the origin of a malfunctioning of the thyroid gland. In some cases, it is also prescribed to people with autoimmune diseases of non-thyroid origin (such as systemic lupus erythematosus, rheumatoid arthritis or pernicious anemia) who show symptoms attributable to thyroid involvement. It can also be prescribed in case of repeated miscarriages or in pregnancy.
The presence of thyroid antibodies mainly indicates an autoimmune thyroid disease and, in particular, if the values are high, it is likely that they are:
- Hashimoto's thyroiditis
- Graves' disease
- idiopathic myxedema of the adult
A more moderate increase in peroxidase antibodies can also be found in other diseases such as:
- thyroid cancer
- thyroid adenoma
- multinodular goiter
- Addison's disease
- type 1 diabetes
- rheumatoid arthritis
- pernicious anemia
- autoimmune collagen diseases
In the presence of slight increases in values, therefore, it is advisable to periodically repeat the analyzes and foresee the possible execution of other tests.
Even in pregnant women with a normally functioning thyroid gland, antibodies to peroxidase (anti-TPO) may be detected, especially in the first trimester. As this could indicate an increased risk of postpartum hypothyroidism, it is suggested that TSH (a pituitary hormone that controls the thyroid) levels be checked every 4 weeks during the second trimester of pregnancy to assess the appropriateness of treatment. Anti-TPOs cross the placenta but no association is observed with thyroid malfunction in the fetus.
In the event of a negative result (ie if the presence of anti-peroxidase antibodies in the blood is not detected but an autoimmune disease is suspected), it is advisable to repeat the test shortly after.
Bibliography
Niguarda Hospital. Laboratory tests. Thyroid peroxidase antibodies
