Stimulated Thyroglobulin Testing Protocol
For stimulated thyroglobulin testing, two methods are available: thyroid hormone withdrawal for 3-4 weeks or administration of recombinant human TSH (rhTSH), with rhTSH being the preferred method due to less morbidity and better quality of life. 1
Methods of TSH Stimulation
Thyroid Hormone Withdrawal Method
- Discontinue levothyroxine (T4) therapy for 3-4 weeks to achieve adequate TSH stimulation (TSH >25-30 mIU/L) 1, 2
- This method results in a larger area under the curve (AUC) of TSH exposure (approximately 4.6 times greater than rhTSH) 3
- Disadvantages include prolonged hypothyroid symptoms, decreased quality of life, and potential time lost from work 2
Recombinant Human TSH (rhTSH) Method
- Administration of 0.9 mg rhTSH intramuscularly for two consecutive days 1, 3
- Blood sampling for thyroglobulin measurement typically 72 hours after the second injection 1
- Advantages include avoiding hypothyroid symptoms and maintaining normal daily activities 1
- Particularly beneficial when thyroid hormone withdrawal is contraindicated (e.g., severe heart disease, advanced age, psychiatric conditions) 1
Timing of Testing
- Stimulated thyroglobulin testing is typically performed:
- 6-12 months after initial treatment (total thyroidectomy and radioiodine ablation if performed) 1
- During follow-up for patients with previously negative TSH-suppressed thyroglobulin but at higher risk for recurrence 1
- When evaluating patients with suspicious findings on imaging or rising thyroglobulin levels 1
Interpretation of Results
- Stimulated thyroglobulin <1 ng/mL with negative antithyroglobulin antibodies indicates excellent response to therapy 1
- Stimulated thyroglobulin 1-10 ng/mL requires continued monitoring and possibly additional imaging 1
- Stimulated thyroglobulin >10 ng/mL warrants consideration of radioiodine therapy (100-150 mCi) and additional imaging 1
Common Pitfalls and Caveats
- Presence of thyroglobulin antibodies can interfere with thyroglobulin measurement, leading to falsely low results 1
- Incomplete thyroid hormone withdrawal (TSH <25 mIU/L) may result in falsely low stimulated thyroglobulin values 2
- Patients with detectable basal thyroglobulin (>0.1 ng/mL but <1.0 ng/mL) on sensitive assays may still benefit from stimulation testing to detect disease 1
- Recent radioiodine administration can temporarily suppress thyroglobulin production, potentially leading to falsely low values 1
Special Considerations
- For patients with high likelihood of requiring radioiodine therapy, thyroid hormone withdrawal is suggested; otherwise, rhTSH is preferred 1
- In patients with distant metastases, consider steroid prophylaxis when using rhTSH stimulation 1
- Newer high-sensitivity thyroglobulin assays (<0.1 ng/mL) may reduce the need for stimulation testing in some low-risk patients 1