Thyroid Peroxidase Antibodies | Thyroglobulin Antibodies

Thyroid Peroxidase Antibodies

Antigens

Thyroid Peroxidase (TPO) has been characterized as an integral membrane hemoprotein (MW around 100 kDa), which catalyzes the iodination of thyroglobulin (TG), as well as the coupling of two di-iodothyrosine residues in the TG molecule to form thyroxine. The actual nature of the "microsomal antigen" remained unknown for nearly three decades, until in 1985 when Portmann et al. could show, that the microsomal antigen is identical to TPO. The sensitivity and specificity of TPO antibodies assays relies heavily on the purity and quality fo the test antigen and in particular on the test antigen and in particular on the absence of TG contaminant.

The Varelisa TPO Antibodies assay and the ImmunoCAP Thyroid Peroxidase use human recombinant TPO, produced in eukaryotic cells (Baculovirus/Sf9 system).

Disease association, antibody prevalence and specificity

• Hashimoto Thyroiditis (91-99%)
• Graves' Disease (71-97%)
• Primary Myxedema (40-70%)
• Post-partum Thyroiditis (60%)
• Subacute Thyroiditis (de Quervain) (very rare)
• Endocrine Orbitopathy (47%)
• Simple Goiter (25%)
• Thyroid Cancer (5%)
• May occur in organ-specific autoimmune diseases, including Pernicious Dnemia, Addison's Disease, type I Diabetes Mellitus, Polyglandular Endocrine Failure Syndromes etc.
• Healthy individuals (5-15%, higher in elderly, but mostly in low titers)

To learn more:

• Information about the diseases

New assays have sensitivities and specificities of >95%. Negative tests can virtually exclude a diagnosis of thyroiditis.

Disease activity

Quantitatively, there is a tendency for individuals with higher autoantibody levels to be more susceptible to hypothyroidism.

When is the measurement recommended?

• Suspicion of Thyroiditis
• Pregnancy in women with familial history of thyroid or autoimmune complications

Antibody isotype

IgG

References

• Rapoport B, McLachlan SM (1996) Thyroid peroxidase autoantibodies. In: Peter JB, Shoenfeld Y (eds.), Autoantibodies, pp 816-821, Elsevier Science B.V., Amsterdam 
• McLachlan SM, Rapoport B (1995) Genetic and epitopic analysis of thyroid peroxidase (TPO) autoantibodies: Markers of the human thyroid autoimmune response. Clin Exp Immunol 101, 200-206 
• Kraiem Z (1998) The measurement of antithyroid autoantibodies in the diagnosis and management of thyroid autoimmune disease. Clin Rev Allergy Immunol 16, 219-225

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Thyroglobulin Antibodies

Antigens

Thyroglobulin (TG) is a large 670 kDa globular glycoprotein composed of two identical disulfide-linked subunits. The majority of thyroid iodine is associated with this prohormone which plays an important role in the biosynthesis of the thyroid hormones T3 and T4. About 75% of the total protein content of the thyroid follicle consists of thyroglobulin. Due to the large TG content of the thyroid gland, a good antigen quality and purity can be achieved using conventional purification techniques.

The Varelisa TG Antibodies assay and the ImmunoCAP Thyroglobulin are coated with thyroglobulin purified from human thyroid glands.

Disease association, antibody prevalence and specificity

• Hashimoto Thyroiditis (60-85%)
• Graves' Disease (30-80%)
• Primary Myxedema (20-30%)
• Post-partum Thyroiditis (30%)
• Subacute Thyroiditis (de Quervain) (very rare)
• Endocrine Orbitopathy (24%)
• Simple Goiter (4%)
• Thyroid Cancers (2-15%)
• Pernicious Anemia (27%)
• Addison's Disease (28%)
• Diabetes Mellitus (20%)
• Healthy Individuals (4-8%, higher in elderly, but mostly in lower titers)

Autoantibodies to TG and TPO provide a valuable exclusionary test in patients with thyroid disease, because over 98% of thyroiditis patients have autoantibodies to either or both of these antigens. Negative tests can virtually exclude a diagnosis of thyroiditis.

Disease activity

Primary risk factor to future autoimmune thyroid dysfunction. A change in TG antibody levels may provide useful information in postoperative patients with differentiated thyroid carcinoma; an elevation of these antibodies could indicate recurrence or metastases.

When is the measurement recommended?

• Suspicion of Thyroiditis
• Differnatioted Thyroid Carcinoma after operation

Antibody isotype

IgG

References

• Burek CL, Rose NR (1996) Thyroglobulin autoantibodies. In: Peter JB, Shoenfeld Y (eds.), Autoantibodies, pp 774-782, Elsevier Science B.V., Amsterdam 
• Kraiem Z (1998) The measurement of antithyroid autoantibodies in the diagnosis and management of antithyroid autoantibodies in the diagnosis and management of thyroid autoimmune disease. Clin Rev Allergy Immunol 16, 219-225 
• Fisher DA, Pandian MR, Carlton E (1987) Autoimmune thyroid disease: An expanding spectrum. Pediatr Clin North Am 34, 907-918

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