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Test ID: TPO    
Thyroperoxidase (TPO) Antibodies, Serum

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Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the diagnosis of thyroid autoimmune disorders

 

Differentiating thyroid autoimmune disorders from nonautoimmune goiter or hypothyroidism

 

As a diagnostic tool in deciding whether to treat a patient who has subclinical hypothyroidism

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Thyroperoxidase (TPO) is an enzyme involved in thyroid hormone synthesis, catalyzing the oxidation of iodide on tyrosine residues in thyroglobulin for the synthesis of triiodothyronine and thyroxine (tetraiodothyronine). TPO is a membrane-associated hemoglycoprotein expressed only in thyrocytes and is one of the most important thyroid gland antigens.

 

Disorders of the thyroid gland are frequently caused by autoimmune mechanisms with the production of autoantibodies. Anti-TPO antibodies activate complement and are thought to be significantly involved in thyroid dysfunction and the pathogenesis of hypothyroidism.

 

The determination of TPO antibody levels is the most sensitive test for detecting autoimmune thyroid disease (eg, Hashimoto thyroiditis, idiopathic myxedema, and Graves disease) and detectable concentrations of anti-TPO antibodies are observed in most patients with these disorders. The highest TPO antibody levels are observed in patients suffering from Hashimoto thyroiditis. In this disease, the prevalence of TPO antibodies is about 90% of cases, confirming the autoimmune origin of the disease. These autoantibodies also frequently occur (60%–80%) in the course of Graves disease.

 

In patients with subclinical hypothyroidism, the presence of TPO antibodies is associated with an increased risk of developing overt hypothyroidism. Many clinical endocrinologists use the TPO antibody test as a diagnostic tool in deciding whether to treat a patient with subclinical hypothyroidism, and Mayo Medical Laboratories endorses this practice.

 

See Thyroid Function Ordering Algorithm in Special Instructions.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

<9.0 IU/mL

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

Values >9.0 IU/mL generally are associated with autoimmune thyroiditis, but elevations are also seen in other autoimmune diseases.

 

In patients with subclinical hypothyroidism, the presence of thyroperoxidase (TPO) antibodies predicts a higher risk of developing overt hypothyroidism, 4.3% per year versus 2.1% per year in antibody-negative individuals. Furthermore, it raises the concern that such patients may be at increased risk of developing other autoimmune diseases, such as adrenal insufficiency and type 1 diabetes.

 

The frequency of detectable anti-TPO observed in nonimmune thyroid disease is similar to the 10% to 12% observed in a healthy population with normal thyroid function.

 

There is a good association between the presence of autoantibodies against TPO and histological thyroiditis. However, in view of the extensive regenerative capacity of the thyroid under the influence of thyroid-stimulating hormone, chronic thyroid disease may be present for years before the clinical manifestation of hypothyroidism becomes evident, if ever.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Moderately increased levels of thyroperoxidase (TPO) antibodies may be found in patients with nonthyroid autoimmune disease such as pernicious anemia, type I diabetes, or other disorders that activate the immune system.

 

Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedure, may have circulating anti-animal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Feldt-Rasmussen U: Analytical and clinical performance goals for testing autoantibodies to thyroperoxidase, thyroglobulin, and thyrotropin receptor. Clin Chem 1996;42:160-163

2. Gharib H, Tuttle RM, Baskin HJ, et al: Consensus Statement #1, Subclinical thyroid dysfunction: a joint statement on management from the American Association of Clinical Endocrinologists, The American Thyroid Association, and The Endocrine Society. Thyroid 2005;15:24-28

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test