Tumor Marker – Part 10 – Thyroglobulin (Tg) as Tumor marker
- Venous blood needed to prepare the serum.
Purpose of the test (Indications)
- This is done to diagnose hyperthyroidism.
- This is the tumor marker for well-differentiated thyroid cancer (follicular and papillary).
- Thyroglobulin is not elaborated by medullary or anaplastic thyroid cancer.
- This can also help to monitor the thyroid cancer or metastatic cancer.
- Make sure that patients are off the thyroid medication for 6 weeks.
- Evaluate the TSH level before testing the Tg.
- Anti-Tg antibodies are present in 15 to 35% of patients with thyroid cancer. These will interfere with the Tg results.
- Thyroglobulin is a glycoprotein, 660kD and iodinated secretion of epithelial cells of the thyroid gland.
- It is synthesized and secreted by the thyroid follicular cells.
- Thyroglobulin is a precursor of the thyroid hormone.
- This may be made by normal epithelial cells and as well as by the cancer cells.
- If there is a very low level of Tg after the surgery of thyroid indicates very little leftover of the thyroid tissues.
- The iodinated secretion also contains T3, T4, and hormones.
- Tg is also called as a tumor marker.
- Half-life is about 65 hours. It takes a nearly month before thyroglobulin becomes undetectable following total thyroidectomy.
- In the operated cases of cancer, Tg postoperatively gives the idea about the activity of the disease and the volume of thyroid tissue left behind.
- The rising level of Tg indicates tumor recurrence and progression.
- Tg is also raised in benign conditions as well, so not specific or sensitive for the diagnosis of thyroid cancer.
- After thyroidectomy, thyroid hormone replacement is needed for normal body metabolism.
- Because of thyroid hormone replacement TSH level is low, so minimal stimulation of thyroid cells.
- To stimulate Tg in thyroid cancer cases after thyroidectomy, stop the hormone replacement for at least 6 weeks.
- Now TSH will be stimulated and this will stimulate Tg production form the epithelial cells.
- If there is any leftover of the thyroid cancer cells then the Tg level will increase.
- After surgery and radiation of cancer patients, the Tg level is undetectable.
- Depletion of hormones is needed because of the Thyrogen-stimulation test.
- Thyrogen is a synthetic purified recombinant source like a human thyroid-stimulating hormone (TSH).
- Thyrogen stimulates the thyroid and will raise the Tg level.
- Normal thyroid tissue and thyroid cancer cells raise >10 times Tg level by TSH stimulation.
- By the hydrogen stimulation test, thyroglobulin (Tg) level will be detectable.
- 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.
|Cord blood||24.4 ± 3.7|
|One hour||29.7 ± 4.2|
|48 hours||41.9 ± 5.8|
|Adult||3 to 42|
- To convert into SI unit x 1.0 = µg/L
- 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.
- 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 the normal adults have serum value of <10 ng/mL.
Increased thyroglobulin level is seen in:
- Thyroid follicular and papillary carcinoma.
- Thyroid adenoma.
- Untreated and metastatic thyroid cancer.
- Subacute thyroiditis, Hashimoto’s thyroiditis, and Grave’s disease.
- Benign thyroid adenoma.
- Recurrence of the metastatic tumor after the treatment.
Decreased Thyroglobulin level is seen in:
- Infants with goiter (Hypothyroidism).
- Thyrotoxicosis factitia.