Endocrine Abstracts

Introduction: The approach for initial thyroid hormone suppression in patients who undergo surgery for differentiated thyroid cancer (DTC), is based upon the risk of disease recurrence. In particular, recent American Thyroid Association guidelines suggest to maintain TSH levels between 0.1 and 0.5 mU/l and less than 0.1 mU/l for patients with ‘intermediate’ and ‘high’ risk respectively. The aim of the study is to identify the major predictive factors of LT4 requirement to obtain semisuppressed or suppressed TSH levels and to elaborate a new method that could improve the accuracy of the LT4 therapeutic starting dose in intermediate and high risk DTC patients.

Methods: Two hundred and nineteen patients who underwent total thyroidectomy and radio-remnant ablation for DTC have been retrospectively evaluated. One hundred and forty nine were on TSH suppressive therapy (TSH<0.1 mU/l) and 70 on TSH semisuppressive therapy (TSH: 0.1–0.4 mU/l). The results obtained by this retrospective analysis were used to formulate a nomogram for the calculation of the LT4 dose.

Results: For both groups (suppressive and semisuppressive LT4 therapy) the best parameters to predict the optimal LT4 starting dose are body mass index (BMI) and age. On the basis of the nomogram, the LT4 dose in μg/kg to obtain suppressed and semisuppressed TSH levels ranged from 1.6 to 2.1 μg/kg per day and from 1.5 to 1.9 μg/kg per day respectively. The dose is higher in younger patients with lower BMI.

Conclusion: In our study BMI and age represent important parameters to predict LT4 dose in intermediate and high risk DTC patients. LT4 requirement decrease with the increase in age and BMI, probably due to the relative decrease of lean body mass. Based on these data, a user-friendly nomogram, representing an efficient method to calculate LT4 starting dose in patients who underwent thyroidectomy for differentiated thyroid cancer, has been created.