TGAB – Overview: Thyroglobulin Antibody, Serum

Lists a shorter or abbreviated version of the Published Name for a test

Indicates the status of NY State approval and if the test is orderable for NY State clients.

A short description of the method used to perform the test

In conjunction with antithyroperoxidase autoantibodies, this test aids in the evaluation of autoimmune thyroiditis (Hashimoto disease).

As an adjunct in the diagnosis of autoimmune thyroid diseases: Hashimoto disease, postpartum thyroiditis, neonatal hypothyroidism, and Graves disease

Suggests clinical disorders or settings where the test may be helpful

Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Identifies specimen types and conditions that may cause the specimen to be rejected

Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

If not ordering electronically, complete, print, and send a General Request (T239) with the specimen.

Patient Preparation: For 12 hours before specimen collection, do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.

Defines the optimal specimen required to perform the test and the preferred volume to complete testing

For the follow-up of patients with differentiated follicular-cell derived thyroid carcinomas, consider ordering HTG2 / Thyroglobulin, Tumor Marker, Serum or HTGR / Thyroglobulin, Tumor Marker Reflex, Serum.

Useful For

Suggests clinical disorders or settings where the test may be helpful

As an adjunct in the diagnosis of autoimmune thyroid diseases: Hashimoto disease, postpartum thyroiditis, neonatal hypothyroidism, and Graves disease

Clinical Information

Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Thyroglobulin autoantibodies bind thyroglobulin (Tg), a major thyroid-specific protein. Tg plays a crucial role in thyroid hormone synthesis, storage, and release.

Tg is not secreted into the systemic circulation under normal circumstances. However, follicular destruction through inflammation (thyroiditis and autoimmune hypothyroidism), hemorrhage (nodular goiter), or rapid disordered growth of thyroid tissue, as may be observed in Graves disease or follicular cell-derived thyroid neoplasms, can result in leakage of Tg into the blood stream. This results in the formation of autoantibodies to Tg (anti-Tg) in some individuals. The same processes also may result in exposure of other “hidden” thyroid antigens to the immune system, resulting in the formation of autoantibodies to other thyroid antigens, in particular thyroid peroxidase (TPO) (anti-TPO). Since anti-Tg and anti-TPO autoantibodies are observed most frequently in autoimmune thyroiditis (Hashimoto disease), they were originally considered to be of possible pathogenic significance in this disorder. However, the consensus opinion today is that they are merely disease markers. It is felt that the presence of competent immune cells at the site of thyroid tissue destruction in autoimmune thyroiditis simply predisposes the patient to form autoantibodies to hidden thyroid antigens.

In individuals with autoimmune hypothyroidism, 30% to 50% will have detectable anti-Tg autoantibodies, while 50% to 90% will have detectable anti-TPO autoantibodies. In Graves disease, both types of autoantibodies are observed at approximately half these rates.

The presence of anti-Tg, which occurs in 15% to 30% of thyroid cancer patients, could result in misleading Tg results. In immunometric assays, the presence of thyroid antibody can lead to false-low measurement; whereas it might lead to false-high results in competitive assays.

Reference Values

Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

<4.0 IU/mL

Reference values apply to all ages.

Interpretation

Provides information to assist in interpretation of the test results

Diagnosis of Autoimmune Thyroid Disease:

Measurements of antithyroperoxidase (TPO) have higher sensitivity and equal specificity to antithyroglobulin (anti-Tg) measurements in the diagnosis of autoimmune thyroid disease. Anti-Tg levels should, therefore, only be measured if anti-TPO measurements are negative, but clinical suspicion of autoimmune thyroid disease is high. Detection of significant titers of anti-Tg or anti-TPO autoantibodies is supportive evidence for a diagnosis of Graves disease in patients with thyrotoxicosis. However, measurement of the pathogenic antithyrotropin (anti-thyroid stimulating hormone)) receptor antibodies by binding assay (THYRO / Thyrotropin Receptor Antibody, Serum) or bioassay (TSI / Thyroid-Stimulating Immunoglobulin, Serum) is the preferred method of confirming Graves disease in atypical cases and under special clinical circumstances.

Positive thyroid autoantibody levels in patients with high-normal or slightly elevated serum thyrotropin levels predict the future development of more profound hypothyroidism.

Patients with postpartum thyroiditis with persistently elevated thyroid autoantibody levels have an increased likelihood of permanent hypothyroidism. 

In cases of neonatal hypothyroidism, the detection of anti-TPO or anti-Tg in the infant suggests transplacental antibody transfer, particularly if the mother has a history of autoimmune thyroiditis or detectable thyroid autoantibodies. The neonatal hypothyroidism is likely to be transient in these cases.

Cautions

Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Antithyroglobulin (anti-Tg) and antithyroid peroxidase (anti-TPO) values determined by different methodologies might vary significantly and cannot be directly compared with one another. Some patients might show to be antibody-positive by some methods and antibody-negative by others. Comparing anti-Tg and anti-TPO values from different methods might lead to erroneous clinical interpretation.

Clinical Reference

Recommendations for in-depth reading of a clinical nature

1 Sapin P, d’Herbomez M, Gasser F, Meyer L, Schlienger JL: Increased sensitivity of a new assay for anti-thyroglobulin antibody detection in patients with autoimmune thyroid disease. Clin Biochem. 2003 Nov;36(8):611-616. doi: 10.1016/s0009-9120(03)00114-0

2. Saravanan P, Dayan CM: Thyroid autoantibodies. Endocrinol Metab Clin North Am. 2001 June;30(2):315-337

3. Baloch Z, Carayon P, Conte-Devolx B, et al: Laboratory Medicine Practice Guidelines. Laboratory support for the diagnosis and monitoring of thyroid disease Thyroid 2003 Jan;13(1):45-67

4. Algeciras-Schimnich A: Thyroglobulin measurement in the management of patients with differentiated thyroid cancer. Crit Rev Clin Lab Sci. 2018 May;55(3):205-218. doi: 10.1080/10408363.2018.1450830

5. Frohlich E, Wahl R: Thyroid autoimmunity: Role of anti-thyroid antibodies in thyroid and extra-thyroidal diseases. Front Immunol. 2017 May 9;8:521. doi: 10.3389/fimmu.2017.00521