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Under normal conditions, thyroglobulin (Tg for short) is a macromolecular glycoprotein (MW = 660000) stored in the thyroid follicle colloid. Thyroglobulin is the prohormone used by the thyroid gland to synthesize T3 and T4. Lysosomes containing proteases cleave T3, T4, and Tg to release T3 and T4. Thyroglobulin (Tg) is the precursor protein for thyroid hormone synthesis and storage carrier.
TgAb originates from lymphocytes in the thyroid gland. It mostly belongs to the G-type immunoglobulin and is mainly composed of various IgG antibodies. It is common in patients with autoimmune thyroid diseases. Therefore, TgAb is a routine serum marker for autoimmune thyroid diseases. TgAb positivity is also found in 10% to 25% of DTC (differentiated thyroid cancer) patients. The normal range of TgAb is 0~115kU/L. Under normal circumstances, TgAb has no damaging effect on the thyroid, but when the thyroid is destroyed on a large scale, TgAb will bind to Fc receptors, thereby activating natural killer cells and causing the destruction of thyroid cells. TgAb levels depend on the duration of antigen exposure, and high Tg levels in the blood do not necessarily induce antibody production. It should be noted that TgAb levels have nothing to do with tumor burden, but the activity of the immune system, so some disease-free patients may not be able to completely achieve TgAb negativity, which may be related to the long-term memory of plasma cells.
Figure 1. TSH regulation of thyroid hormone biosynthesis in thyroglobulin. (Citterio CE, et al.; 2019)
Thyroglobulin is present in the serum of healthy individuals. When thyroid tissue is inflamed and damaged, its concentration in the serum increases. In addition, Hashimoto (chronic lymphocytic thyroiditis CLT), Graves (viral diffuse goiter), thyroid adenoma, subacute thyroiditis, thyroid cancer, etc. can all have elevated Tg levels.
Serum thyroglobulin concentration can also reflect thyroid mass, thyroid damage, and TSH receptor activation. When patients have goiter or are in a state of hyperthyroidism, serum Tg increases. Abnormally elevated serum Tg concentrations are due to abnormal thyroid mass, excessive stimulation of the thyroid gland, or physical damage to the thyroid gland secondary to surgery, fine needle aspiration, or thyroiditis.
In the case of differentiated thyroid cancer (DTC), serum Tg concentration reflects thyroid mass (tumor or normal residual tissue), thyroid damage (surgery or FNA), and TSH receptor activation. Because TSH levels are the primary regulator of serum Tg concentration, it is difficult to interpret serum Tg values without knowing the patient's TSH status. Although there is no "normal Tg reference range" for patients undergoing treatment for DTC, the normal relationship between thyroid mass and serum provides an important reference point. When serum TSH levels are normal, 1 g of normal thyroid tissue can specifically release 1 μg/L Tg into the circulation; if serum TSH is suppressed below 0.1 mU/L, it releases only 0.5 μg/L Tg.
In addition, Tg is also a major indicator after thyroidectomy. In patients who have had thyroidectomy and do not have thyroglobulin antibodies in their blood, thyroglobulin can reflect the condition of these patients. Tg testing is mainly used for follow-up of patients after total or subtotal thyroidectomy. Since the thyroid is the only known source of Tg, after total or subtotal thyroidectomy with successful radioactive iodine ablation of residual thyroid tissue, serum Tg concentrations will drop to very low or even undetectable levels. For patients who have undergone partial thyroidectomy, the Tg level detected depends on how much thyroid tissue remains after surgery. If Tg can still be detected after total thyroidectomy, it indicates DTC residue or recurrence. Therefore, a significant increase in Tg often indicates recurrence of the disease.
In addition to tumors, elevated Tg concentrations have been reported in different thyroid diseases, such as Hashimoto's disease, Graves' disease, etc. Tg also plays an important role in the differentiation of subacute thyroiditis and factitious thyrotoxicosis. In addition, for congenital hypothyroidism, Tg detection can be used to distinguish congenital absence of thyroid gland from thyroid hypoplasia or other pathological conditions.
Thyroxine synthesized by the thyroid is also stored in the follicular cavity after being combined with thyroglobulin. When the body needs it, thyroxine is detached from thyroglobulin and secreted into the blood. Generally, thyroid cells do not actively release thyroglobulin into the blood, but some thyroglobulin always "leaks" into the blood. Therefore, thyroglobulin can also be measured in the blood, but in smaller amounts. Differentiated thyroid cancer cells also have functions similar to normal thyroid cells and can also secrete Tg. Many thyroid cancer patients will pay attention to the indicator Tg thyroglobulin after popular science studies, but ignore the unknown but very important project of TG-Ab thyroglobulin antibody.
TG-Ab is a thyroglobulin antibody. When talking about antibodies, we must first talk about the antigen. The antigen of TG-Ab is Tg. When Tg is released into the blood, the body's immune cells do not recognize it, and lymphocytes produce corresponding antibodies TG- Ab.
Clinically, 20%-30% of thyroid patients have positive serum thyroglobulin antibody TG-Ab. Normally, TG-Ab levels in patients with differentiated thyroid cancer will also gradually decrease to very low levels after total thyroidectomy (patients with Hashimoto's disease before surgery will decrease slowly or not at all). If the TG-Ab level rises again or continues to rise above the original level, it often indicates the possibility of tumor recurrence or metastasis.
TG-Ab can combine with Tg. Therefore, the detection of serum Tg will be directly affected by the level of TG-Ab in the body. When TG-Ab is very high, the measured Tg will be lower than the true value, affecting the accuracy of Tg. When TG-Ab is at a very low level (negative), Tg has greater reference significance. If the serum TG-Ab level remains unchanged, it is considered undeterminable, and imaging examinations are required for further investigation.
Therefore, when detecting Tg, TG-Ab should be detected at the same time, and Tg and TG-Ab detection reagents from the same manufacturer should be selected to avoid differences caused by kit designs from different manufacturers to ensure the accuracy of the test results.
Serum Tg is the main serological indicator of prognosis of DTC, but when TgAb is positive, Tg measurement is greatly reduced, and its role as a serum tumor marker is limited. Therefore, TgAb-positive DTC patients should have their serum TgAb levels detected before and after surgery and 131I treatment to provide clinicians with more laboratory data as a reference. TgAb can be measured by direct, non-competitive and competitive assays. They use different detection tools: immunoenzyme, radioimmunoassay, immunochemiluminescence and immunofluorescence.
Reference
| Target | Cat. No. | Product Name | Expression System | Tag/Conjugate | Application | |
| Thyroglobulin | DAGA-826 | Human thyroglobulin (Controls grade,>96%) | Human thyroid glands | Unconjugated | Controls, Calibrators, ELISA, Blotting | Inquiry |
| DAGA-824 | Human thyroglobulin (> 99%) | Human thyroid glands | Unconjugated | N/A | Inquiry | |
| DAG4833 | Human Thyroglobulin | Human thyroid glands | Unconjugated | WB, ELISA | Inquiry |
| Target | Cat. No. | Product Name | Size | Species Reactivity | Application | Detection Sample | |
| Thyroglobulin | DEIA096J | Thyroglobulin recovery ELISA Kit | 96T | Human | Quantitative | plasma, serum | Inquiry |
| DEIA273 | Human thyroglobulin IgG ELISA Kit | 96T | Human | Quantitative | serum, plasma | Inquiry | |
| DEIA273 | Human thyroglobulin IgG ELISA Kit | 96T | Human | Quantitative | serum, plasma | Inquiry | |
| DEIA7554 | Anti-TG ELISA Kit | 96T | Human | Quantitative | serum, plasma | Inquiry | |
| DEIACL62 | CDSimple™ Thyroglobulin Chemiluminescent ELISA Kit | 96T | Quantitative | Serum | Inquiry |
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