Prediction of LT4 replacement dose to achieve euthyroidism in subjects undergoing total thyroidectomy for benign thyroid disorders.

Background: Total thyroidectomy is becoming the preferred choice of treatment in patients with benign disorders of the thyroid gland; hence, an optimal method of replacing thyroxine is essential to avoid the ill effects of over- and under-replacement of thyroxine in such patients.

Patients And Methods: We analyzed three methods of thyroxine replacement: replacement per kilogram of lean body mass (LBM) (2.5 mcg/kg LBM per day), per kilogram of body weight (1.6 mcg/kg body weight per day), and empirical replacement of thyroxine.

Results: The thyroxine requirement in thyroidectomized patients was 2.04 mcg/kg per day, with an increasing requirement of thyroxine with increments of weight. On multivariate analysis we found that the thyroxine requirement was strongly correlated both with body surface area (BSA) and with body weight. On subsequent correlation testing, we found that BSA was more strongly associated than weight with the thyroxine requirement.

Conclusions: Patients undergoing total thyroidectomy may require higher doses of thyroxine to achieve euthyroidism when compared to patients with similar anthropometric parameters having primary hypothyroidism. The method of replacing thyroxine based on LBM is the ideal method, but replacement based on fixed-dose regimens could be a good method if the body weight is taken into consideration.