What is TG in blood?

This is an automatically translated article.

The article was professionally consulted by MSc Do Thi Hoang Ha - Doctor of Biochemistry, Laboratory Department - Vinmec Hai Phong International General Hospital
TG is synthesized by thyroid follicular cells and released into the serum along with thyroid hormones. TG index is used as a tumor marker to evaluate the effectiveness of thyroid cancer treatment and to monitor recurrence of differentiated thyroid cancers.

1. What is the TG in the blood?

Thyroglobulin, also abbreviated as Tg, is an iodine-containing glycoprotein with a molecular weight of more than 660kDa, the main component of the colloid of thyroid follicles, secreted into the cavity of the thyroid follicles, a small part of the week. return to the blood. Tg is an important substrate for iodine binding to tyrosin in the synthesis of thyroid hormones T3 (Tri-iodo-thyronin) and T4 (Thyroxin). The most important physiological stimulator for thyroglobulin synthesis and release is the thyroid stimulating hormone (TSH) of the anterior pituitary gland. The half-life of Tg in plasma is 2-4 days.
Tg is only synthesized by normal thyroid follicular cells or/by papillary carcinoma cells and cancer cells of thyroid follicular so in thyroid cancer, differentiated cancer, the Tg concentration in serum is usually elevated.
The Tg test is used to evaluate the effectiveness of thyroid cancer treatment and to monitor recurrence of differentiated thyroid cancer. There are 2 most common types of cancer, papillary thyroid cancer and follicular thyroid cancer, which often increase Tg production, so the amount of Tg in the blood also increases. In addition, patients are often prescribed Tg tests by doctors to diagnose other diseases and give more accurate results, for example, on patients with symptoms of hyperthyroidism or thyroid enlargement..

2. When is a Tg test ordered?

2.1 In the diagnosis of thyroid diseases Tg test is indicated in the diagnosis of 2 types of thyroid cancer, which are follicular and papillary. This test combines testing for TSH (a thyroid-stimulating hormone) before undergoing thyroid cancer treatment. The purpose of the test is to check if serum Tg levels are higher than normal. If serum Tg levels are high, periodic testing is needed to check for recurrence of the disease after treatment.
In addition, this test is also indicated to determine the cause of hyperthyroidism as well as to monitor the course and effectiveness of Graves' treatment with antithyroid drugs over time. A combination of Tg, Anti-TG, and Anti-TPO tests will help your doctor find out whether the cause of your hypothyroidism is due to thyroid autoantibodies.
Tg can also be used to differentiate between subacute thyroiditis from drug-induced thyrotoxicosis and to determine the cause of congenital hypothyroidism in children
2.2 In the treatment and monitoring of recurrent thyroid cancer Indication of TG test before and after surgery to evaluate the effectiveness of the treatment process. Test results help determine if surgery has removed all of the cancerous tumors.
The TG and Anti-TG tests are often used in combination to monitor cancer recurrence. In the case of patients with thyroid cancer, but with complicated, persistent disease and low serum Tg levels and positive anti-Tg levels, it is necessary to stimulate Tg with recombinant human TSH thyroid-stimulating hormone (TSH). rhTSH (recombinant human TSH) can detect recurrence of cancer.

3. Meaning of TG . test

The normal human Tg value is 0.2 to 70 ng/mL, however this value can vary depending on the test kit used by the laboratory. 48 hours after birth, Tg levels can reach 36 to 38 ng/mL. In the general population, the average 9% of people will have low Tg values ​​below 10 ng/mL. The normal value of Anti-Tg is less than 115 IU/mL in all age groups.
The value of Tg can be increased or decreased in the following cases:
3.1. An increase in TG An increased TG value indicates some of the following:
Untreated differentiated thyroid cancer or metastatic cancer. Note Tg is not elevated in anaplastic (undifferentiated) and medullary thyroid carcinomas among other rare cancers. Sensitivity to detect Tg at the postoperative stage is highest when the tumor size is less than 2cm and the preoperative Tg level is very high. If before surgery, the patient's Tg level is within the normal range, the Tg test result should not be used to evaluate the effectiveness of treatment. After surgery or chemotherapy, the amount of Tg will increase if there is a recurrence of the disease. In the first 10 years after treatment, more than 10% of patients relapse and this rate decreases to 5% in the following years. Tg can be increased in some benign thyroid diseases as follows: Basedow, benign lymphoma, liver failure, benign thyroid tumor, acute thyroiditis,... 3.2. The amount of Tg decreases The amount of Tg can be reduced in the following cases:
Hypothyroidism due to goiter in children. Artificial thyroid toxicity. Congenital absence of thyroid gland After total thyroidectomy

4. Some other things to watch out for about TG . testing

The Tg test is not used to screen for thyroid cancer in large numbers of the asymptomatic population due to the very low prevalence of thyroid cancer in Vietnam. In women, this ratio is 27/1 million and in men it is 13/1 million.
This test is also not used to confirm the diagnosis of thyroid cancer, but this is only a test to support the diagnosis as well as evaluate the effectiveness of treatment and monitor thyroid cancer recurrence. To diagnose thyroid cancer, it is necessary to perform a biopsy method and then observe the thyroid tissue under a microscope. Performing Tg and Anti-Tg tests at the same time for accurate test results because over 15% of thyroid cancer patients are able to self-produce anti-Tg and Anti-Tg antibodies combined with Tg will lead to the deviation of the true value of Tg.
Briefly, Tg is synthesized by thyroid follicular cells and released into the serum along with thyroid hormones. Tg index is used as a tumor marker to evaluate the effectiveness of thyroid cancer treatment and to monitor recurrence of differentiated thyroid cancers.
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