Serum Thyroglobulin (Tg)

Specimen Required

Fasting Required

Purpose of the Test

To monitor treatment of some types of thyroid cancer and to look for return of the cancer

When this test is required

A thyroglobulin test may be requested after the surgical removal of your thyroid gland for cancer so your doctor can check for any normal and/or cancerous thyroid tissue that may have been left behind. It is often checked on a regular basis, even if negative after surgery, to make sure that the tumour has not come back or spread.

What the Test Detects

The thyroid gland is a small butterfly shaped organ that helps to regulate the rate at which the body uses energy. The thyroid lies flat against the windpipe in the throat and is composed primarily of very small, ball-shaped structures called follicles. This test measures the amount of thyroglobulin in the blood.Thyroglobulin is a protein produced by follicle cells and stored in the thyroid gland. Thyroglobulin is broken down to release the thyroid hormones T4 (thyroxine) and T3 (triidothyronine) when needed. The production of these hormones and their release into the blood stream is stimulated by the hormone TSH (thyroid stimulating hormone). No other part of the body makes thyroglobulin, but it is produced by many thyroid cancers – both those confined to the thyroid gland and those that have spread to other parts of the body. Thyroglobulin is a tumour marker but concentrations in the blood can be increased in other thyroid disorders.See MoreSee Less

Preparation for the Test

No fasting or special preparation is required before the test. In order to increase the ability of the test to pick up very small amounts of remaining thyroid cells some patients may be asked to stop taking their thyroid hormone replacement tablets prior to the test or be given injections (recombinant TSH) in an attempt to stimulate thyroglobulin production. Dietary supplement rich in vitamin B7 (Biotin) should not be taken in the day before the test in order to avoid test interference that many lead to false results. Please follow any instructions you are given by your Doctor, prior to having this blood test.

Sample Requirements

A blood sample taken from a vein in your arm

Additional Notes

Elevated concentrations of thyroglobulin do not in themselves imply a bad outcome. In monitoring for cancer recurrence, change over time is more important than one particular thyroglobulin test result.It is important to have serial thyroglobulin tests performed at the same laboratory because test methods may produce different results in different laboratories.Fifteen to twenty percent of thyroid cancer patients (1 in 5) have thyroglobulin antibodies (also called thyroglobulin autoantibodies). These antibodies can lead to falsely high or low thyroglobulin results depending on the method used.

Selected Tests