Tg Antibodies Rising

This is information I compiled related to questions concerning Thyroglobulin Antibodies (TgAb)
remaining elevated or increasing following total thyroidectomy despite having low or undetectable
Thyroglobulin (Tg) and whether TgAb can be used to detect recurrence of thyroid cancer.

Elevated Thyroglobulin Antibodies (TgAb) in the absence of elevated Tg levels

  • Thyroglobulin is uniquely produced by thyroid follicular cells.
  • Biotin can falsely lower Thyroglobulin test results.
  • Earlier IMA and Mass Spectrometry tests may not be sensitive enough to detect low levels of Thyroglobulin and may still be in use. Current LabCorp Tg is sensitive down to 0.2 ng/mL and Quest Diagnostics to 0.4 ng/mL.
  • Thyroglobulin Antibody (TgAb) trends can be used as a surrogate thyroid cancer tumor marker. Presence of TgAb indicates that thyroid tissue is present, high levels are prognostic for recurrence..
  • Related: If low Tg preoperatively, Tg may not rise in the presence of recurrent disease.

Biotin can falsely lower Tg
Biotin Interference in Assays for Thyroid Hormones, Thyrotropin and Thyroglobulin – PubMed


https://pubmed.ncbi.nlm.nih.gov/21917876/ (2011, so before Mass Spec) indicates TgAb trend importance.
Conclusions:Patients with Hashimoto’s thyroiditis frequently have TgAb detected and may have a higher risk for papillary thyroid cancer. Although TgAb interferes with Tg IMA measurements, TgAb trends can be used as a surrogate DTC tumor marker in preference to Tg IMA, provided that the same method is used.


More sensitivity is always better: Measuring sub-clinical levels of serum thyroglobulin on a μLC– MS/MS system
Although liquid chromatography–tandem mass spectrometry (LC–MS/MS) assays for thyroglobulin (Tg) are resistant to autoantibody (TgAb) interference, recent studies have demonstrated approximately 40% of TgAb-positive individuals with recurrent thyroid cancer have Tg concentrations below the lower limit of quantification (LLOQ) of the LC–MS/MS assays described to date (i.e., <0.5 ng/mL), resulting in false-negative findings during post-thyroidectomy monitoring.


Use of thyroglobulin as a tumour marker
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5329716/
Hypothesis that low Tg prior to surgery may invalidate it’s use as a tumor marker post surgery. Kind of related in a secondary fashion.
It may not be able to see high serum TG after thyroidectomy if the TG level before surgery had been low or normal. Therefore, it is necessary to recognise patients who would not have rising TG in the presence of recurrence before using TG as a tumour marker. This can only be done if the serum TG level before the surgery is known. Those who have normal or low serum TG before surgery will not show rising serum TG when there is recurrence of disease[16]. This happens irrespective of the anti-TGAb status of the patient


Prognostic value of change in anti-thyroglobulin antibodies after thyroidectomy in patients with papillary thyroid carcinoma
>Changes in TgAb levels in the first year after surgery can predict the risk of persistence/recurrence of TgAb-positive PTC patients. Patients who achieved negativization of TgAb presented an excellent prognosis.


Sequential changes of serum antithyroglobulin antibody levels are a good predictor of disease activity in thyroglobulin-negative patients with papillary thyroid carcinoma
Methods:
In 56 patients followed for more than 7 years, we recorded all serum TgAb levels (except the ones determined within one year after (131)I therapy or diagnostic scans) and evaluated their disease status. All patients had undergone total thyroidectomy and remnant ablation by (131)I, and they were positive for TgAb and had undetectable thyroglobulin during follow-up. The sequential changes of TgAb were defined as persistently high, increasing, persistently medium, decreasing, and decreasing to negative. Recurrence or persistence of PTC was defined as active disease as assessed by (131)I scanning, (18)F-fluorodeoxyglucose positron emission tomography, ultrasonography, computed tomography, or surgical examination.
Conclusion:The presence of TgAb is indicative of an active tumor. Sequential TgAb change is a good predictor of disease prognosis and is helpful for clinical decision making.


Clinical outcome of patients with differentiated thyroid cancer and raised antithyroglobulin antibody levels: a retrospective study
Patients with recurrences had very high baseline TgAb > 1000 IU/ml.
[LabCorp 0.0-0.9 IU/mL Sonora Quest <41 IU/mL Goal is undectable]


Thyroglobulin Antibody Normal Range + High Levels
(This is a compilation, not a research study.)
Other autoimmune disorders can trigger TgAb’s but must have thyroid tissue present in the first place.
Other factors, ranging from other autoimmune conditions to certain medications and supplements, that can affect TgAb.