Thyroid autoantibodies: interpretation and assay interference
THE CONTEXT
Thyroid antibody measurements help establish the cause of thyroid dysfunction and thyroid swellings.
Antibodies in autoimmune thyroiditis
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Antibodies against thyroid peroxidase (TPO) and thyroglobulin help determine the cause of thyroid dysfunction and swellings.
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Autoimmune thyroiditis may present with thyroid toxicity, thyroid failure or a euthyroid goitre.
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TPO antibody levels above 25 units/mL and antithyroglobulin titres greater than 1:100 are considered significant.
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Some patients with histological evidence of lymphocytic autoimmune thyroiditis are seronegative.
Assay interference and Graves’ disease
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Antithyroglobulin antibodies interfere with serum thyroglobulin assays, which has implications for thyroid cancer follow-up.
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Thyroid-stimulating hormone receptor antibodies, termed TSH-RAb or TRAB, are often present in Graves’ disease and are largely produced within the thyroid itself.