Also Known As
Tg
TGB
Formal Name
Thyroglobulin, Serum or Plasma
This article was last reviewed on
This article waslast modified on
May 25, 2018.
At a Glance
Why Get Tested?

To monitor treatment of thyroid cancer and to detect recurrence; less commonly, to help determine the cause of hyperthyroidism and hypothyroidism

When To Get Tested?

Prior to and after the completion of treatment for thyroid cancer, before and after radioactive iodine therapy, and at regular intervals to monitor for recurrence; it may be ordered in conjunction with other thyroid tests for certain thyroid disorders.

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Usually none; 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, your healthcare practitioner should inform you if this or any other preparation is necessary.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

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 serves as the source of T4 and T3. The production of these hormones and their release into the bloodstream are stimulated by the pituitary hormone TSH (thyroid stimulating hormone).

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.

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.

Accordion Title
Common Questions
  • How is it used?

    The thyroglobulin test is primarily used as a tumor marker to evaluate the effectiveness of treatment for thyroid cancer and to monitor for recurrence. Not every thyroid cancer will produce thyroglobulin, but the most common types, the well-differentiated papillary and follicular thyroid cancers, frequently do, resulting in increased levels of thyroglobulin in the blood.

    Thyroglobulin testing may be used, along with a TSH test, prior to thyroid cancer treatment to determine whether the cancer is producing thyroglobulin. If it is, then the test can be ordered at intervals after treatment to monitor for cancer recurrence. Several thyroglobulin levels may be ordered over a period of time (serial samples) to look at the change in concentration. The change often provides more information than a single value.

    Thyroglobulin testing is also occasionally ordered to help determine the cause of hyperthyroidism and to monitor the effectiveness of treatment for conditions such as Graves disease.

    Rarely, the test may be ordered to help differentiate between subacute thyroiditis and thyrotoxicosis factitia and to determine the cause of congenital hypothyroidism in newborns.

  • When is it ordered?

    A thyroglobulin test may be ordered prior to the surgical removal of the thyroid gland for cancer. It is also ordered after the completion of treatment to help determine whether any normal and/or cancerous residual thyroid tissue may have been left behind. It is often ordered on a regular basis after surgery to make sure that the tumor has not come back or spread (monitor for recurrence and/or metastasis).

    A thyroglobulin test may sometimes be ordered when a person has symptoms of hyperthyroidism and/or an enlarged thyroid gland and the healthcare practitioner suspects that the person may have a thyroid disorder such as Graves disease or thyroiditis. It may be ordered at intervals when someone is being treated with anti-thyroid medications (for conditions such as Graves disease) to determine the effectiveness of treatment.

    Rarely, it may be ordered when an infant has symptoms associated with hypothyroidism.

  • What does the test result mean?

    Thyroglobulin is present in the blood of all healthy individuals at very low concentration.

    If thyroglobulin concentrations are initially elevated in a person diagnosed with thyroid cancer, then it is likely that thyroglobulin can be used as a tumor marker.

    Thyroglobulin levels should be undetectable or very low after the surgical removal of the thyroid (thyroidectomy) and/or after subsequent radioactive iodine treatments. However, if upon monitoring post-surgery the thyroglobulin concentration in the person's blood is still detectable, there may still be some normal or cancerous residual thyroid tissue in the person's body, indicating the need for additional treatment.

    Based on the results of a thyroglobulin test, a healthcare practitioner may follow up with a radioactive iodine scan and/or radioactive iodine treatments to identify and/or destroy any remaining normal thyroid tissue or thyroid cancer. Thyroglobulin levels are then checked again in a few weeks or months to verify that the therapy has worked and monitored periodically there afterwards.

    If the level of thyroglobulin is low for a few weeks or months after surgery but then begins to rise over time, then the cancer is probably recurring or spreading (metastasis).

    Decreasing levels of thyroglobulin in those treated for Graves disease indicate a response to treatment.

    People who have a goiter, thyroiditis, or hyperthyroidism may have elevated thyroglobulin levels, although the test is not routinely ordered with these conditions.

  • Is there anything else I should know?

    Increased concentrations of thyroglobulin are not diagnostic of thyroid cancer. Cancer must be diagnosed by looking at samples of cells (biopsy) under a microscope. Elevated levels of thyroglobulin do not in themselves imply a poor prognosis. In monitoring for cancer recurrence, change over time (pattern) is more important than one particular thyroglobulin test result.

    Laboratories may use different methods to test for thyroglobulin, so results can vary from lab to lab. If you are having a series of thyroglobulin tests done (several tests done on different days), it is advised that you have the tests done by the same method, typically by the same laboratory, so that the results can be compared and interpreted correctly. You may wish to discuss this issue with your healthcare provider.

    Thyroglobulin antibodies (TgAb) are immune proteins produced that target thyroglobulin. Depending on the test method used by the laboratory, these antibodies can interfere with the results of the thyroglobulin test if they are present in the blood of the person being tested. If the antibodies are present, either the Tg test cannot be used to monitor levels or a method that is not affected by TgAb must be used to monitor levels. Read the article on Thyroid Antibodies to learn more.

    Those who have their thyroid removed will need to take thyroid hormone replacement (thyroxine) for the rest of their life. In the past, a healthcare practitioner may have had someone on thyroxine refrain from taking it for up to several weeks prior to thyroglobulin testing. This is because low thyroxine will stimulate the production of TSH and, in turn, this will stimulate the production of thyroglobulin by any remaining normal or cancerous thyroid tissue. Therefore, cessation of thyroxin therapy will make the thyroglobulin test more sensitive, but it often leaves the person being tested with uncomfortable hypothyroid symptoms until testing is completed. A recombinant form of TSH is now available as an alternative. It is used to directly stimulate thyroglobulin production.

  • Should everyone have a thyroglobulin test?

    No. This test is not intended to be a screening test for the general public. It is not specific for thyroid cancer and can be temporarily elevated with many thyroid conditions, both benign and malignant.

  • Why didn't my doctor check my thyroglobulin level before removing my thyroid?

    Your thyroglobulin (Tg) level may or may not be measured before your thyroid gland is removed as part of the treatment for thyroid cancer. Since the protein is produced by normal thyroid tissue as well as by many thyroid cancers and can be elevated with many thyroid conditions, it can be difficult to determine whether an increased thyroglobulin is due to the cancer.

  • Is there anything I can do to raise or lower my thyroglobulin level?

    No, not directly. This test reflects the presence of normal and/or cancerous thyroid tissue and is not affected by lifestyle changes.

  • Can thyroglobulin testing be performed in my healthcare practitioner's office?

    No, it requires specialized equipment to perform. The test may not be offered in every laboratory and may need to be sent to a reference laboratory. Due to certain technical limitations of the assay, normal reference ranges can vary greatly. Thus, when serial thyroglobulin levels are required, they should be performed at the same laboratory.

View Sources

Sources Used in Current Review

2016 review performed by Alina G. Sofronescu, PhD, NRCC-CC, FACB.

Mayo Medical Laboratories. Thyroglobulin, Tumor Marker Reflex to LC-MS/MS or Immunoassay. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/62936. Accessed on 10/13/2016.

Clarke, William. Contemporary Practice in Clinical Chemistry. 2nd Ed, AACC Press, 2011. Pp. 501-502.

(March 31, 2016) American Cancer Society. Tests for Thyroid Cancer. Available online at http://www.cancer.org/cancer/thyroidcancer/detailedguide/thyroid-cancer-diagnosis. Accessed on 10/25/2016.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Schlumberger, M. and Baudin, E. (1998). Serum Thyroglobulin determination in the follow-up of patients with differentiated thyroid carcinoma. European Journal of Endocrinology [On-line journal], vol (138) Pp 249-252. PDF available for download at http://www.eje.org/eje/138/0249/1380249.pdf.

What is Thyroglobulin? John Hopkins Thyroid Tumor Center [On-line information]. Available online through http://www.thyroid-cancer.net.

Spencer, C. Thyroglobulin (Tg) and Tg Antibody (TgAb) Testing for Patients Treated for Thyroid Cancers. Thyroid Cancer Survivors' Association, Inc. [On-line article]. Available online at http://www.thyca.org/thyroglobulin.htm.

ARUP. Thyroglobulin and Thyroglobulin Antibody. ARUP lab [On-line testing information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_215b.htm.

ACS (2001 July 5). All About Thyroid Cancer, Detailed Guide. American Cancer Society [On-line information]. Available online at http://www.cancer.org/eprise/main/docroot/cri/cri_2_3x?dt=43.

(2001 November 23). Antithyroglobulin antibody. MedlinePlus [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003557.htm.

ATA (2002). Cancer of the Thyroid. The American Thyroid Association [On-line information]. Available online at http://www.thyroid.org/resources/patients/brochures/thyroid_cancer.html.

(© 2005). Cancer of the Thyroid. American Thyroid Association [On-line information]. PDF available for download at http://www.thyroid.org/patients/brochures/ThyroidCancer_brochure.pdf.

Whitley, RJ and Ain, KB (2004). Thyroglobulin: a specific serum marker for the management of thyroid carcinoma. Medscape from Clin Lab Med. 2004; 24(1):29-47 (ISSN: 0272-2712) [On-line Abstract] Available online at http://www.medscape.com/medline/abstract/15157556?queryText=thyroglobulin.

Liebert, M.A. (2003 June 05). Thyroid Tests for the Clinical Biochemist and Physician Thyroglobulin (Tg) Measurement. Medscape from Thyroid 13(1):57-67, 2003. [On-line information]. Available online at http://www.medscape.com/viewarticle/452669_print.

(© 2006). Thyroglobulin and Thyroglobulin Antibody. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.arup-lab.com/guides/clt/tests/clt_249b.jsp#1149079.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 916-918.

Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 372.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 1030-1031.

(Revised 2009 May 14). How Is Thyroid Cancer Diagnosed? American Cancer Society [On-line information]. Available online at http://www.cancer.org/docroot/cri/content/cri_2_4_3x_how_is_thyroid_cancer_diagnosed_43.asp?sitearea=&level=. Accessed October 2009.

Grebe, S. (2009 March 25). Diagnosis and Management of Thyroid Carcinoma: A Focus on Serum Thyroglobulin. Medscape Today from Expert Review of Endocrinology and Metabolism [On-line information]. Available online at http://www.medscape.com/viewarticle/586810. Accessed October 2009.

Hershman, J. (Reviewed 2008 June). Thyroid Disorders, Introduction. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec12/ch152/ch152a.html?qt=thyroglobulin&alt=sh. Accessed October 2009.

Hoofnagle, A. and Wener, M. H. (2006 December). Serum thyroglobulin: a model of immunoassay imperfection. Clinical Laboratory International, CLI-Online.com v8 [On-line information]. PDF available for download at http://www.cli-online.com/fileadmin/artimg/serum-thyroglobulin-a-model-of-immunoassay-imperfection.pdf. Accessed October 2009.

Hershman, J. (Revised 2012 May). Overview of Thyroid Function. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed August 2013.

(© 1995-2013). Thyroglobulin, Tumor Marker, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/83069. Accessed August 2013.

Poduval, J. (Updated 2012 October 5). Thyroglobulin. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2089532-overview. Accessed August 2013.

Chadwick, B. et. al. (Updated 2013 May). Thyroid Cancer. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/ThyroidCancer.html?client_ID=LTD#tabs=0. Accessed August 2013.

(Revised 2013 January 17) How is thyroid cancer diagnosed? American Cancer Society [On-line information]. Available online at http://www.cancer.org/cancer/thyroidcancer/detailedguide/thyroid-cancer-diagnosis. Accessed August 2013.

(2010 January). Thyroid Function Tests. National Endocrine and Metabolic Diseases Information Service [On-line information]. Available online at http://www.endocrine.niddk.nih.gov/pubs/thyroidtests/thyroidtests_508.pdf. Accessed August 2013.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 934-935.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 501-502.

McPherson, R. and Pincus, M. (© 2011). Henry's Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 378-379.

Spencer C. Assay of thyroid hormones and related substances. Thyroid Disease Manager. Pp 1-93. Jan 1, 2013. Available online at http://www.thyroidmanager.org/chapter/assay-of-thyroid-hormones-and-related-substances/. Accessed August 2013.

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