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The Test Sample
What is being tested?
Thyroglobulin (Tg) is a protein produced by the thyroid gland. This test measures the amount of thyroglobulin in the blood.
The thyroid gland produces hormones (thyroxine or T4 and triiodothyronine or T3) that help to regulate the rate at which the body uses energy. It is a small, butterfly-shaped organ that lies flat against the windpipe in the throat and is composed primarily of very small, ball-shaped structures called follicles that produce and store thyroglobulin.
Thyroglobulin is produced all healthy individuals, and normally its concentration in blood is very low. Thyroglobulin concentration increases in both benign (Graves disease, subacute thyroiditis, Hashimoto thyroiditis) and malignant conditions (thyroid adenoma, thyroid papillary and follicular cancer). Therefore, it is on one hand a non-specific indicator of a thyroid dysfunction and, on the other hand, a tumor marker that can be used to monitor patients with thyroid papillary and follicular cancer after diagnosis (see Thyroid Cancer).
How is the sample collected for testing?
A blood sample is 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?
Usually no preparation is needed. However, depending on the laboratory method used for measurement of thyroglobulin, some dietary supplements such as multivitamins or supplements rich in vitamin B7 (Biotin) should not be taken at least 12 hours before the test is performed in order to avoid any test interference that may lead to false results.
Based on information provided by the lab, the healthcare practitioner should inform you if this or any other preparation is necessary.