The Anti-TG test is a chemiluminescent immunoassay (CLIA), for use on IDS automated analyzers. It is used for the quantitative determination of the specific IgG antibodies directed against thyroglobulin, in human samples of serum or plasma (EDTA, Heparin or Na-Citrate).
The autoimmune thyroid diseases (TA) are the most frequent among all autoimmune diseases. In the blood of patients with thyroid disease it is possible to isolate abnormal antibodies, which create self-toxicity phenomena attacking the gland and compromising its correct functionality. The assay of these antibodies is useful to recognize the basis of autoimmune thyroid disease and to distinguish them from other forms that do not affect the immune system 1,2.
The anti-thyroid antibodies used in clinical practice are those acting in particular against thyroglobulin (anti-TG) and thyroid peroxidase (anti-TPO, initially known as microsomal antibodies).
High levels of these antibodies are recorded both in chronic Hashimoto3 thyroiditis and in Graves-Basedow’s disease; the distinction between the two diseases is however easy since the first is typically associated with hypothyroidism, while the Graves-Basedow’s disease typically correlates with hyperthyroidism.
The thyroglobulin 4 is a glycoprotein molecule, precursor of thyroid hormones (thyroxine T4 and triiodothyronine: T3), synthesized through the iodine organification in its tyrosine residues by the thyroid peroxidase enzyme.
Anti-TG autoantibodies are present in the majority of patients with chronic Hashimoto’s thyroiditis or postpartum thyroiditis. They are present also in 30% of patients with Graves-Basedow disease. The test can be positive even in patients with thyroid cancer or other forms of thyrotoxicosis, and in carriers of non-thyroid autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, diabetes mellitus type 1, atrophic gastritis and Addison’s disease. Also pregnancy may be associated to the appearance of anti-thyroglobulin antibodies in the blood.
Thyroid peroxidase (TPO) 5 is an enzyme concentrated in the thyroid follicular cells, essential for the synthesis of thyroid hormones T4 and T3 from thyroglobulin. Anti-TPO autoantibodies are found in the serum of almost all patients with chronic Hashimoto’s thyroiditis and in about half of people with Graves-Basedow disease. Similar to what was considered for the anti-thyroglobulin autoantibodies, high antibody titres are also present in patients with organ-specific non-thyroid diseases and in about 10% of normal individuals. A similar situation occurs during pregnancy, for which there is an increased risk of developing postpartum thyroiditis in case of anti-thyroid peroxidase positivity in the first quarter. Also peculiar of Graves-Basedow disease are anti-thyroid antibodies acting against the TSH6 receptor, the pituitary hormone that stimulates the gland to synthesize thyroid hormones; it is the stimulation of these receptors induced by antibodies that enhance the synthesis of T3 and T4, configuring the typical context of hyperthyroidism often associated with goiter.
Slightly or moderately elevated levels of anti-thyroid antibodies can also be observed in healthy patients, with a normal thyroid function; these individuals must still be monitored over time, since an increased risk of future thyroid disease related to the presence of these antibodies is determined 7,8.
- Weetman AP. Determinants of autoimmune thyroid disease. Nat Immunol 2001; 2: 769-70.
- Tozzoli R, Villalta D, Kodermaz G, Bagnasco M, Tonutti E, Bizzaro N. Autoantibody profiling of patients with autoimmune thyroid disease using a new multiplexed immunoassay method. Clin Chem Lab Med 2006; 44: 837-42.
- Gilmour J, Brownlee Y, Foster P, Geekie C, Kelly P, Robertson S, et al. The quantitative measurements of autoantibodies to thyroglobulin and thyroid peroxidase by automated microparticle based immunoassays in Hashimoto’s disease, Graves’ disease and a follow –up study on post-partum thyroid disease. Clin Lab 2000; 46: 57-61.
- Okesieme OE, Parkes AB, Premawardhama LD, Evans C, Lazarus JH. Thyroglobulin: current aspects of its role in autoimmune thyroid disease and thyroid cancer. Minerva Med 2003; 94: 319-30.
- McLachlan SM, Papoport B. Thyroid peroxidase as an autoantigen. Thyroid 2007; 10: 939-48.
- Adams HD, Purves DD. Abnormal responses in assay of thyrotropin. Proc Univ Otago Sch Med 1956; 34:11-2.
- Prummel MF, Wiersinga WM. Thyroid peroxidase autoantibodies in euthyroid subjects. Best Pract Res Clin Endocrinol Metab 2005; 19:1-15.
- Jensen EA, Pedersen PH, Blaabjerg O, Hansen PS, Brix TH, Hegedus L. Establishment of reference distribution and decision values for thyroid antibodies against thyroid peroxidase (TPOAb), thyroglobulin (TgAb) and thyrotropin receptor (TRAb). Clin Chem Lab Med 2006; 44: 991-8.