From the Guidelines
Management of patients with high thyroglobulin (Tg) antibodies requires careful monitoring and specialized testing approaches, prioritizing ultrasound surveillance of the neck every 6-12 months and considering periodic whole-body radioiodine scans. The presence of these antibodies interferes with standard thyroglobulin measurement, making it unreliable for cancer surveillance 1. For these patients, serial measurement of the Tg antibody levels themselves can serve as a surrogate tumor marker, as declining antibody levels often correlate with successful treatment while persistent or rising levels may indicate residual disease.
Key Considerations
- In post-thyroidectomy patients being monitored for thyroid cancer recurrence, additional imaging such as neck CT, MRI, or FDG-PET scans may be warranted if there is clinical suspicion of recurrence despite negative ultrasound findings 1.
- Treatment decisions should not be based solely on Tg antibody levels but on comprehensive clinical assessment, considering the American Thyroid Association risk categories of recurrence to guide imaging and management 1.
- The interference from Tg antibodies occurs because they form complexes with thyroglobulin in the blood, causing falsely low or undetectable Tg measurements in immunometric assays or potentially falsely elevated results in radioimmunoassays, making standard monitoring protocols ineffective for these patients.
Surveillance and Treatment Approach
- Ultrasound surveillance of the neck every 6-12 months is recommended, alongside periodic whole-body radioiodine scans, to monitor for recurrence in patients with high Tg antibodies 1.
- For patients with suspected recurrence of differentiated thyroid cancer, the approach should be guided by the risk category, with more aggressive imaging and treatment strategies considered for high-risk patients 1.
- Treatment options for recurrence may include neck dissection, repeat RAI therapy, external beam radiotherapy, and systemic therapy, depending on the extent and location of the disease 1.
From the Research
Management Approach for High Thyroglobulin Antibodies
- The presence of high thyroglobulin antibodies (TgAb) can interfere with the measurement of thyroglobulin (Tg) levels, making it challenging to monitor thyroid cancer progression and recurrence 2.
- In patients with high TgAb, the American Thyroid Association does not recommend serum Tg after thyroid hormone withdrawal or recombinant human thyrotropin administration (stimulated Tg) and diagnostic whole-body scanning (DxWBS) if Tg values while on thyroxine (Tg-on-T4) are <1 ng/mL 3.
- However, some studies suggest that performing stimulated Tg and DxWBS can be useful in detecting persistent disease in patients with TgAb who appear to be free of disease after total thyroidectomy and radioactive iodine ablation 3.
- The combination of PET and computed tomography can increase the diagnostic accuracy and reduce pitfalls in detecting metastatic disease, especially in patients with low or dedifferentiated thyroid cancer 4.
- Liquid chromatography-tandem mass spectrometry (LC-MS/MS) can be used to measure Tg levels in patients with high TgAb, as it is not affected by the presence of antibodies 2.
Clinical Implications
- High TgAb levels are associated with an increased risk of thyroid cancer in patients with thyroid nodules 5.
- The presence of TgAb can lead to false-negative or false-positive results in Tg measurements, making it essential to consider alternative diagnostic methods 2.
- Clinicians should be aware of the potential interference of TgAb with Tg measurements and consider the use of LC-MS/MS or other diagnostic methods to accurately assess thyroid cancer progression and recurrence 2, 3.