Adequate Thyroid-Stimulating Hormone Levels After Levothyroxine Discontinuation in the Follow-Up of Patients with Well-Differentiated Thyroid Carcinoma

Background follow-up of patients with well-differentiated thyroid carcinomas (WTC), a thyroid-stimulating hormone (TSH) ≥30 μU/mL is generally accepted as adequate to perform whole body scans (WBS), determine thyroglobulin (Tg), and administer radioiodine therapeutically. These patients, inevitably rendered hypothyroid, are traditionally switched to T3 for 3–4 weeks prior to withdrawing all thyroid hormones for an additional 2–3 weeks. Neither TSH and Tg elevation dynamics nor WBS characteristics after simply interrupting L-T4 treatment without T3 administration have been evaluated. s otal T4 and T3, as well as FT4 were measured weekly after discontinuing L-T4 in 21 subjects (group I) and after thyroidectomy in 10 subjects (group II). WBS and Tg determination was performed upon achievement of TSH ≥30 μU/mL. s second week, 42% of group I patients and 70% of group II patients had TSH ≥30 μU/mL. By the third week, 90% in group I and 100% in group II had achieved this target. Group I patients who needed 4 weeks to increase TSH received a greater cumulative radioiodine dose and had higher Tg levels. Positive WBS were found in eight cases and the incidence of a negative WBS with elevated Tg was significantly higher when evaluation occurred at the second week of L-T4 withdrawal compared to the fourth week. sions nterruption is a reasonable alternative to temporary T3 in preparation for radioiodine scanning and treatment.