Antithyroglobulin Antibodies In Serum

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Contents 1 Reference-interval 2 Principle 3 Clinical-significance 4 Specimen 5 More General Terms 6 Additional Terms 7 References

Reference-interval

• < 20 U/ mL ()
• < 5 U/ mL ( ELISA)
• results dependent on area of residence & disease state

Principle

• Proteins such as thyroglobulin are readily bound to the surface of red blood cells which have been treated with tannic acid. Thyroglobulin extracted from human thyroid glands by classical salt precipitation techniques coupled to tanned turkey red cells provides a hemagglutination test system for the detection of low levels of antibody to thyroglobulin. A small proportion of human sera is reactive against turkey erythrocytes, giving rise to non-specific agglutination of the sensitized cells. These non- specific reactions may be detected by means of unsensitized Control Cells. Both Test & Control Cells are treated with formalin & freeze-dried to give long term stability on storage.

Clinical-significance

• associated with: (also see thyroglobulin autoantibody)

• autoimmune thyroid disease
• Hashimoto's thyroiditis
• atrophic thyroiditis (myxedema)
• thyrotoxicosis ( Graves disease)

• frequently assessed in combination with anti thyroid microsomal antibodies
• combined absence of anti-thyroglobulin & anti-thyroid microsomal antibodies virtually rules out autoimmune thyroid disease
• in patients with subclinical hypothyroidism, presence of anti-thyroglobulin antibodies confers an increased risk of developing overt hypothyroidism [2]
  

• Passive hemagglutination tests ( HA) for autoantibodies to thyroglobulin are about 1,000 times more sensitive than precipitin test, & Hashimoto patients with positive precipitins gave HA titers or 640 to many millions. The combination of thyroglobulin & microsomal hemagglutionation tests will detect practically all Hashimoto goiters & about 90% of primary myxedema cases.
  
• The two tests should be performed together on all cases of goiter scheduled for operation as it is not always possible clinically to distinguish autoimmune thyroiditis from other types of goiter. Another important application of the two thyroid antibody tests is in the differential diagnosis of primary thyrotoxicosis & various tachycardias, anxiety stages, unexplained weight loss or diarrhea. In cases with unilateral exophthalmos the tests will help to differentiate between an endocrine etiology & local orbital lesions, obviating more invasive or expensive tests.
  
• About 70-90% of cases with variants of Graves' disease gave positive thyroglobulin &/or microsomal hemaglutination titers compared with 10-15% of controls according to age & sex.
  
• Although most thyrotoxic subjects show relatively low levels of antibody, about 20% have moderate to high titers (Thyroglobulin > 1:640, Microsomal >1:6400) & this indicates either a more severe form of the disease with a tendency to relapse, or a concomitant destructive thyroiditis predisposing to post-operative myxedema or to spontaneous loss of thyroid function some years after the thyrotoxic episode. Similarly, thyroglobulin in combination with microsomal hemagglutination will distinguish between atrophic thyroiditis with mild or severe hypothyroidism & cases of depression or obesity due to other causes. Positive results in these 2 tests are not sufficient to exclude thyroid cancer, nor are low titers (Thyroglobulin <1:160, Microsomal <1:1600) always indicative of severe thyroid lesions, as many cases of 'focal thyroiditis' remain subcinical & non-progressive. If a positive result is obtained, supplementary investigations such as thyroid scintiscans for cancer, TRH tests for thyroid autonomy or serum TSH estimations for suspected hypothyroidism are necessary, the choice of test being dependent on the clinical findings.
  
• Thyroglobulin & microsomal hemagglutination tests give useful predictive evidence of possible thyroid destruction in patients with other autoimmune endocrine disorders such as Addison's disease, insulin-dependent diabetes mellitus or polyendocrine autoimmune disorders, & in members of families prone to organ-specific autoimmunity.

Specimen

• serum
• plasma samples are not suitable for testing
• infected serum samples are unsuitable for testing
• blood collected by venipuncture should be allowed to clot naturally & the serum clarified by centrifugation before testing
• store at -20 degrees C

More General Terms

• serology

Additional Terms

• anti-thyroglobulin antibody
• thyroglobulin; Tg (TG)

References

1. Package Insert, Thymune-T, Wellcome Diagnostics, Research Triangle Park, N. C. 27709.
2. Tietz, Norbert W., Textbook of Clinical Chemistry, W. B. Saunders, Co., Philadelphia, 1986, p 1136.
3. Clinical Guide to Laboratory Tests, 3rd edition, NW Tietz ed, WB Saunders, Philadelphia, 1995
4. Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009

anti-thyroglobulin antibodies in serum