Thyroglobulin is a protein that is produced by follicular cells in the thyroid gland. Most tumours that start from follicular cells in the thyroid gland also produce thyroglobulin. The follicular cells use this protein to make and store the thyroid hormones T3 and T4.
Pathologists use a test called immunohistochemistry to ‘see’ thyroglobulin protein inside the tissue sample. Most thyroglobulin is found inside small round spaces called follicles. Doctors can also perform a test to look for thyroglobulin in the blood. This test is usually performed after someone has had their thyroid gland removed. The level of thyroglobulin decreases after the thyroid gland is removed and is usually undetectable after several weeks. Increasing levels of thyroglobulin in the blood after surgery may be a sign that tumour is still present somewhere in the body.
Positive for thyroglobulin means that the thyroglobulin protein was seen in the tissue sample. Reactive is another term that pathologists use to describe cells that are producing thyroglobulin.
Negative for thyroglobulin means that the thyroglobulin protein was not seen in the tissue sample. Non-reactive is another term that pathologists use to describe cells that are not producing thyroglobulin.
Pathologists often perform immunohistochemistry for thyroglobulin to determine if the cells that they are seeing under the microscope come from the thyroid gland. This is particularly important when examining tumour cells that have spread to another part of the body (this type of spread is called a metastasis). If the tumour cells are positive for thyroglobulin, it suggests that the tumour may have started in the thyroid gland or may be made up of cells that are behaving like cells from the thyroid gland. In contrast, if the cells are negative for thyroglobulin, it suggests that the tumour may have come from cells that do not normally produce thyroglobulin.