Synonyms

   Antithyroid Antibodies, Microsomal Antibodies

Clinical Significance

    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

Specimen

   Serum

Stability

   Refrigerated (preferred) : 7 days

   Frozen : 30 days

   Ambient : 7 days

Reference Range

   ≤ 34 IU/ml

Interpretation

   Values above 34 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.

Limitation

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