Influence of Lean Body Mass and Disease Etiology on Levothyroxine Requirements in Patients with Hypothyroidism

Objective: It was aimed to evaluate the dose requirement depending on the etiology and to compare lean body mass and total body weight in the calculation of drug dose in patients receiving levothyroxine sodium replacement. Material and Method: A total of 124 patients who were receiving levothyroxine sodium treatment for total thyroidectomy, hypothyroidism due to radioactive iodine therapy treatment and autoimmune hypothyroidism were included in cross-sectional study. Patients' drug doses, height, weight, thyroid stimulating hormone, T4 and T3 values were recorded on the hospital documentation system. Lean Body Mass was calculated and the doses of drugs were calculated based on total body weight and Lean Body Mass. Patients were separated into 3 groups as normal weight, overweight and obese according to body mass index. Results:Patients with Hashimoto's thyroiditis required lower daily levothyroxine doses compared to those who had undergone total thyroidectomy. Similarly, the daily levothyroxine dosage per kilogram of lean body mass and total body weight was significantly lower in the Hashimoto's group than in the total thyroidectomy group. While the RAI group showed intermediate values that did not differ significantly from either group Conclusion: This study shows that the use of lean body mass is more significant than body mass index in determining the dose of levothyroxine in hypothyroid patients. Findings show that the dose of levothyroxine varies according to the etiology of hypothyroidism and that treatment doses should be determined accordingly.