Thyroglobulin (Tg)

Sample for Thyroglobulin (Tg)

• Venous blood is needed to prepare the serum.

Purpose of the test (Indications) for Thyroglobulin (Tg)

1. Thyroglobulin is advised after the treatment of thyroid cancer.
2. This is done to diagnose hyperthyroidism.
3. This is the tumor marker for well-differentiated thyroid cancer (follicular and papillary).
   1. Thyroglobulin is not elaborated by medullary or anaplastic thyroid cancer.
4. This can also help to monitor thyroid cancer or metastatic cancer.

Precautions for Thyroglobulin (Tg)

1. Make sure that patients are off the thyroid medication for 6 weeks.
2. Evaluate the TSH level before testing the Tg.
3. Anti-Tg antibodies are present in 15 to 35% of patients with thyroid cancer. These will interfere with the Tg results.

Pathophysiology of Thyroglobulin (Tg)

1. Thyroglobulin is a glycoprotein, 660kD, and iodinated secretion of epithelial cells of the thyroid gland.
   1. It is synthesized and secreted by the thyroid follicular cells.

2. Thyroglobulin is a precursor of the thyroid hormone.
3. This may be made by normal epithelial cells as well as by cancer cells.
4. Raised values of thyroglobulin (Tg) are found in the following:
   2. Thyrotoxicosis.
   3. Thyroiditis.
   4. Iodine deficiency.
   5. Benign thyroid adenomas.
   6. Differentiated thyroid carcinomas (follicular and papillary carcinoma and papillary-follicular carcinoma).
      2. Medullary carcinoma does not produce thyroglobulin (Tg).
5. If there is a very low level of Tg after the surgery of the thyroid indicates very little leftover in the thyroid tissues.
6. The iodinated secretion also contains T3, T4, and hormones.

Thyroglobulin (Tg) is also called a tumor marker.

1. Half-life is about 65 hours (another reference days 8 to 22 hours).
2. It takes nearly a month before thyroglobulin becomes undetectable following total thyroidectomy.
3. In the operated cases of cancer, Thyroglobulin (Tg) postoperatively gives the idea about the activity of the disease and the volume of thyroid tissue left behind.
4. The rising level of Thyroglobulin (Tg) indicates tumor recurrence and progression.
   1. Thyroglobulin (Tg) is also raised in benign conditions as well, so not specific or sensitive for the diagnosis of thyroid cancer.
5. After thyroidectomy, thyroid hormone replacement is needed for normal body metabolism.
   1. Because of thyroid hormone replacement, TSH level is low, so there is minimal stimulation of thyroid cells.
   2. To stimulate Thyroglobulin (Tg) in thyroid cancer cases after thyroidectomy, stop the hormone replacement for at least 6 weeks.
      1. Now TSH will be stimulated, stimulating Thyroglobulin (Tg) production from the epithelial cells.
      2. If there are any leftover thyroid cancer cells, the Thyroglobulin (Tg) level will increase.
      3. After surgery and radiation in cancer patients,  the Thyroglobulin (Tg) level is undetectable.

Advantages of thyroglobulin in cancer patients:

1. A thyroid tumor scan with I¹³¹ is required to differentiate begin and cancer cells.
2. Thyroglobulin estimation advantage is less exposure to radiation in the form of I¹³¹.
3. With thyroglobulin estimation, I¹³¹ is not needed.
4. Patients with metastasis are not detected by the I¹³¹ scan, where thyroglobulin (Tg) is raised.

Thyrogen-stimulation test.

1. Thyrogen is a synthetic purified recombinant source like a human thyroid-stimulating hormone (TSH).
2. Thyrogen is synthetic TSH and is called thyrotropin alpha.
3. Keep the patient off the hormone replacement therapy.
4. Thyrogen two injections are given on two consecutive days.
5. Take a blood sample of the patient for thyroid hormones and thyroglobulin.
6. Normal thyroid tissue and thyroid cancer cells raise >10 times Tg level by TSH stimulation.
   1. Thyrogen stimulates the thyroid gland and raises the thyroglobulin (Tg) level.
7. Advantages of thyrogen test:
   1. It monitors patients who have undergone thyroid surgery.
   2. It can detect residual tumors.
   3. It helps to determine the proper dosage of hormone replacement therapy.

Presence of antithyroglobulin antibodies:

1. Anti-thyroglobulin antibodies are present in 10% of the normal population and 20% of those with thyroid cancer and are a major issue in thyroglobulin testing.

Normal Thyroglobulin (Tg)

Source 1

• To convert into SI unit x 1.0 = µg/L

Male Thyroglobulin (Tg)

• 0 to 11 months = 0.6 to 5.5 ng/mL.
• 1 to 11 years = 0.6 to 50.1 ng/mL.
• Adult = 0.5 to 53 ng/mL.

Female Thyroglobulin (Tg)

• 1 to 11 months = 0.5 to 5.5 ng/mL.
• 1 to 11 years = 0.5 to 52.1 ng/mL.
• Adult = 0.5 to 43 ng/mL.
• Another source gives normal values as follows:
  • Adult = 3 to 42 ng/mL.
  • Newborn = 36 to 48 ng/mL.
  • 87% of normal adults have a serum value of <10 ng/mL.

Increased Thyroglobulin (Tg) level is seen in:

1. Thyroid follicular and papillary carcinoma.
2. Thyroid adenoma.
3. Untreated and metastatic thyroid cancer.
4. Subacute thyroiditis, Hashimoto’s thyroiditis, and Grave’s disease.
5. Benign thyroid adenoma.
6. Hypothyroidism.
7. Recurrence of the metastatic tumor after the treatment.

Decreased Thyroglobulin (Tg) level is seen in:

1. Infants with goiter (Hypothyroidism).
2. Thyrotoxicosis factitia.

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