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Thyroid Peroxidase Antibody

Autoantibodies to thyroid antigens can cause thyroid tissue injury that leads to transient hyperthyroidism and long-term hypothyroidism. Thyroid antibodies include antibody to thyroglobulin and microsomal proteins. Measurement of antimicrosomal antibodies is a more sensitive test for diagnosis of thyroiditis. Measurement of antimicrosomal antibodies is especially useful in confirming a diagnosis of subclinical hypothyroidism in patients with elevated serum TSH concentration and normal free T4 concentration. Between 5 and 25% of patients with high titer antimicrosomal antibodies convert to overt hypothyroidism each year. Antimicrosomal antibodies are almost always detectable in patients with Hashimoto thyroiditis, atopic thyroiditis, and postpartum thyroiditis. Antimicrosomal antibodies are also present in many cases of Graves disease. Antibody is seldom detectable in nonautoimmune thyroid diseases.

The improved sensitivity and specificity of current antimicrosomal antibody assays obviates the need to test for anti-thyroglobulin antibody. Caution must be exercised in interpreting positive results because 10% of adults may have low titers of thyroid antibodies and no symptoms.

Reference range is <35 U/mL.

Specimen requirement is one SST tube of blood.

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