A patient with differentiated thyroid cancer (DTC) undergoes post-thyroidectomy radioiodine (131I) ablation. The serum thyroglobulin (Tg) is measured after TSH stimulation. If the Tg is <0.2 ng/mL with negative anti-Tg antibodies, it indicates:
- A Incomplete thyroidectomy — repeat surgery needed
- B Excellent response — no evidence of structural or biochemical disease ✓
- C High-risk recurrence — adjuvant external beam radiotherapy needed
- D Medullary thyroid cancer recurrence
Correct answer: B. Excellent response — no evidence of structural or biochemical disease
Explanation
Post-ablation, stimulated serum Tg <0.2 ng/mL (with negative anti-Tg antibodies) is defined as an excellent biochemical response to therapy, indicating no residual differentiated thyroid tissue. This is the treatment goal after thyroidectomy + 131I ablation. Elevated Tg or rising Tg indicates structural recurrence requiring whole-body scan and possible additional 131I or targeted therapy. Anti-Tg antibodies can falsely suppress Tg levels, so their absence is required for valid interpretation.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.