What is thyroglobulin?
Thyroglobulin is a protein formed in the thyroid gland. It binds the thyroid hormones T3 and T4 and stores them.
When needed, the hormones split off from thyroglobulin again and can then perform their functions. They are involved in the regulation of many important body functions. Among other things, thyroid hormones affect the cardiovascular system and metabolism.
When do you measure thyroglobulin?
Physicians use thyroglobulin primarily as a tumor marker in thyroid cancer follow-up: If thyroglobulin can still be found in the blood after surgical removal of the thyroid gland, (degenerate) thyroid tissue is still present or has returned.
The second question in which this blood value plays a role is the suspicion of athyreosis in newborns. Physicians understand this to mean the congenital, complete absence of the thyroid gland.
What are the normal values for thyroglobulin?
In healthy people, only a small amount of thyroglobulin is found in the blood. How much is considered normal depends on the measurement method used in the laboratory.
Often, a normal range of three to 40 nanograms per milliliter (ng/ml) of blood is given for healthy adults. This applies to people with a thyroid gland.
Stimulation with rhTSH
In order to obtain the most meaningful values, thyroglobulin is often measured after stimulation with rhTSH (recombinant human thyrotropin). rhTSH stimulates the production of thyroglobulin if thyroid tissue is still present. The test is therefore more sensitive than without stimulation.
When is thyroglobulin elevated?
Thyroglobulin is especially elevated when thyroid tissue increases (grows) or is inflamed. Therefore, the laboratory value is elevated mainly in thyroid cancer (especially papillary and follicular thyroid carcinoma).
However, thyroglobulin levels in the blood may also be elevated in some benign thyroid diseases.
Because various diseases can cause elevated thyroglobulin levels, physicians do not make a diagnosis based on this reading alone.
Elevated levels in thyroid cancer
After the complete thyroid gland with the tumor has been surgically removed in thyroid cancer patients (thyroidectomy), thyroglobulin determination is used to monitor the success of the therapy:
Falsified values due to thyroglobulin antibodies
It should be noted that some thyroid cancer patients form antibodies against thyroglobulin (TG antibodies, Tg-AK). These eliminate thyroglobulin in the blood. In such cases, therefore, no thyroglobulin is found in the blood even if cancerous tissue is still present after the operation. Therefore, the physician additionally examines the blood for TG antibodies.
Elevated levels in benign diseases
The blood level of thyroglobulin may be elevated, for example, in goiter (goiter) and Graves’ disease (Graves’ disease). The same is true in an autonomous thyroid adenoma. This is a thyroid nodule that produces thyroid hormones detached from the body’s own regulatory mechanism, causing hyperthyroidism.
When is thyroglobulin too low?
Decreased thyroglobulin concentrations are found, for example, in people receiving thyroid hormone therapy. The production of thyroid hormones and thyroglobulin is coupled to feedback mechanisms. Drug-induced thyroid hormone suppresses the body’s own production.
Thyroglobulin levels are also zero in congenital absence of the thyroid gland (congenital athyreosis). Athyreosis is the congenital complete absence of the thyroid gland.
What to do if thyroglobulin values change?
Thyroglobulin is not a very specific laboratory value and deviates from the normal values in many thyroid diseases. If values change, you should talk to your doctor about the possible cause and how to proceed.
