Function of the Antibodies to Thyroperoxidase (Anti-TPO) test:
This test is primarily used in the differential diagnosis of thyroid diseases, such as Hashimoto thyroiditis and chronic lymphocytic thyroiditis (in children).
What are Thyroid antibodies?
Thyroid microsomal antibodies are commonly found in patients with various thyroid diseases. They are present in 70% to 90% of patients with Hashimoto thyroiditis. Microsomal antibodies are produced in response to microsomes escaping from the thyroid epithelial cells surrounding the thyroid follicle. These escaped microsomes then act as antigens and stimulate the production of antibodies.
These immune complexes initiate inflammatory and cytotoxic effects on the thyroid follicle. This test is often performed in conjunction with the antithyroglobulin antibody test, which greatly increases the specificity and sensitivity. Although many different thyroid diseases are associated with elevated antimicrosomal antibody levels, the most frequent is chronic thyroiditis (Hashimoto thyroiditis in the adult and lymphocytic thyroiditis in children and young adults). Both of these chronic inflammatory diseases have been associated with other autoimmune (collagen-vascular) diseases. Twelve percent of normal females and 1% of normal males have positive antimicrosomal antibodies. The most sensitive assay for antimicrosomal antibodies is for the antithyroid peroxidase (anti-TPO) antibody.
Anti-TPO is often performed in conjunction with the antithyroglobulin antibody test. When this is done, the specificity and sensitivity are greatly increased. Anti-TPO is present in almost all patients with Hashimoto thyroiditis, in more than 70% of those with Graves disease, and, to a variable degree, in patients with non-thyroid autoimmune disease. Anti-TPO correlates with the degree of lymphocytic infiltrations (inflammation) in the thyroid. Among healthy people, 5% to 10% have elevated anti-TPO levels.
Test Results And Clinical Significance:
What are normal ranges?
Titer <35 IU/mL
Increased Levels
Chronic thyroiditis (Hashimoto thyroiditis): Antimicrosomal antibodies attack the microsome in the thyroid cells. The immune complex creates an inflammatory and destructive process in the gland, which is mediated through the complement system.
Rheumatoid arthritis (RA), Rheumatoid-collagen disease: The association with other autoimmune diseases is well known. The mechanism of this association, however, is not well known.
Pernicious anemia: Anti–parietal cell antibodies have been associated with the presence of antimicrosomal antibodies.
Thyrotoxicosis, Hypothyroidism, Thyroid carcinoma: Microsomes that leak out of the thyroid as a result of the presence of these destructive diseases stimulate the immune system to produce antimicrosomal antibodies.
Myxedema: Antithyroid microsomal antibodies destroy the thyroid cell, resulting in hypofunction of the gland.
References:
- ANTI–TSH RECEPTOR ANTIBODIES IN CLINICAL PRACTICE, https://www.sciencedirect.com/science/article/pii/S0889852905701353?via%3Dihub
- Autoimmune thyroid disease: new models of cell death in autoimmunity, https://www.nature.com/articles/nri750
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Significance of (sub)clinical thyroid dysfunction and thyroid autoimmunity before conception and in early pregnancy: a systematic review , https://academic.oup.com/humupd/article/17/5/605/761372
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