Thyroglobulin Test

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Formal name: Thyroglobulin (Tg)
Related tests: Thyroglobulin antibody; Tumour markers; TSH; Thyroxine (T4)

At a Glance

Why Get Tested?

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

When to Get Tested?

Once treatment for thyroid cancer has been completed, before and after radioactive iodine therapy for thyroid cancer, and at varying intervals to monitor for recurrence.

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

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. Please follow any instructions you are given by your Doctor, prior to having this blood test.

The Test Sample

What is being tested?

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 when needed into the thyroid hormones T4 (thyroxine) and T3 (triidothyronine). 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.

How is the sample collected for testing?

A blood sample is usually obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed, but please follow any instructions you are given by your Doctor, prior to having this blood test.

The Test

Common Questions

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.