Optimal levothyroxine dose in post-total thyroidectomy patients: a prediction model for initial dose titration

As the lack of consensus in the initial levothyroxine (LT4) dose titration following total thyroidectomy exists, the aim of this study was to identify and quantify predictive factors for LT4 dose replacement.

A retrospective analysis of a prospectively gathered data of 234 patients who underwent total-thyroidectomy at two institutions between November 9, 2009 and January 1, 2016 was conducted. Outcome variable was the clinically observed optimal LT4 dose. Linear and polynomial regression methods were used for prediction. Continuous variables were tested for mean differences using Student's t-test and association using Pearson's correlation.

We identified Body Surface Area (BSA) as the most significant predictor. We propose a model that titrates LT4 dose based on BSA (1.4 µg /kg/day for BSA > 1.79 m² vs. 1.7 µg /kg/day for BSA ≤ 1.79 m²; P = 0.00). Men required higher doses than women and no differences were noted based on DM status or pathological diagnosis.

Our analysis shows BSA as an independent predictor of LT4 dose post total thyroidectomy. Despite the possibility of generating different equations for predicting LT4 post total-thyroidectomy, finding a practical and clinically relevant prediction model is yet of limited efficiency.