Duration of levothyroxine discontinuation and pre-radioiodine TSH levels in thyroid cancer.

Abstract

IntroductionRadioiodine treatment in differentiated thyroid carcinoma requires elevated TSH levels to optimize the uptake of [131I]NaI. Levothyroxine suspension is the usual strategy for inducing endogenous TSH elevation, although the optimal duration of this suspension remains controversial.ObjectiveTo evaluate the effect of the duration of levothyroxine suspension on TSH levels achieved prior to radioiodine treatment.Materials and methodsRetrospective cohort study that included 104 patients with differentiated thyroid carcinoma treated at a reference university center. Patients were classified according to the time of discontinuation of levothyroxine prior to radioiodine treatment: three weeks (group A, n = 21) and four weeks (group B, n = 83). TSH levels between groups and their distribution by categories (ResultsThe mean age (SD) was 46.7 (10.3) years and 87 patients were women. The mean TSH was 70.9 mIU/L (95% CI: 54.5-87.2) in group A and 88.7 mIU/L (95% CI: 84.8-92.6) in group B. The proportion of patients who achieved TSH ≥ 30 mIU/L was significantly higher in group B (100% vs 76.2%; p ConclusionsThree weeks of levothyroxine suspension allowed TSH levels ≥30 mIU/L to be reached in most patients, although a proportion did not reach the recommended threshold. Four weeks were associated with adequate TSH elevation in all patients in this cohort. TSH monitoring during preparation could allow for more individualized strategies that optimize thyroid stimulation, minimizing unnecessary exposure to hypothyroidism.