Thyroglobulin Testing When You Have Positive Antibodies (TgAb}
Thyroglobulin (Tg) is produced only by thyroid tissue and is the primary marker for follow up thyroid cancer detection after total thyroidectomy. It is not generally used after a partial or hemi-thyroidectomy as the remaining thyroid lobe will still produce normal levels of thyroglobulin.
If you have thyroglobulin antibodies (TgAb) they will interfere with your Tg test. In this case you should have the mass spectrometry version (LCMS/MS) done for thyroglobulin. It is a more expensive test but necessary if you have antibodies. Some large institutions and cancer centers have their own in house tests to account for antibodies.
It’s advised to have Tg tested at the same laboratory by the same method each time for ongoing monitoring and to stop using supplements containing biotin as biotin can interfere with the test.
Lab Corp provides this test:
Thyroglobulin Antibody and Thyroglobulin, IMA or LC/MS-MS
“Thyroglobulin antibody (TgAb) testing is performed on all samples. If TgAb is negative, serum thyroglobulin is measured by a sensitive IMA with a relatively rapid turnaround time, generally two to three days. If TgAb is positive, serum thyroglobulin is measured by a sensitive LC/MS-MS method. This method is less prone to interference by TgAb but has a longer turnaround time of four to six days.”
Quest Diagnostics, offers this test:
Test code 90814 Thyroid Cancer (Thyroglobulin) Monitor.
Thyroid Cancer (Thyroglobulin) Monitor – Thyroglobulin measurements are most useful in the postoperative monitoring of patients with papillary, follicular, and Hurthle cell carcinomas. However, approximately 20% of individuals develop autoantibodies to thyroglobulin. Since these antibodies interfere with immunoassay measurement of thyroglobulin, it is necessary to determine the presence or absence of antibodies before measuring thyroglobulin. This panel provides a sensitive method for determination of thyroglobulin autoantibodies, with subsequent measurement of thyroglobulin by either a sensitive immunoassay (Tg Ab negative samples) or LCMSMS (Tg Ab positive samples). The mass spectrometry assay has no interference from autoantibodies.
If Thyroglobulin Antibody is negative, then Thyroglobulin is tested on the Beckman Coulter DxI (CPT code: 84432).
If Thyroglobulin Antibody is positive, then Thyroglobulin is tested by LC/MS/MS (CPT code: 84432).
You can print out this page or print the laboratory pages to show your care provider as some may not be aware of the difference or of the availability of the mass spec test. Depending on what part of the country you are in the sample may be sent to a more central specialized lab.