The effectiveness of levothyroxine starting doses after thyroidectomy is compromised by early body variations occurring after surgery

Background: Dosing levothyroxine (LT4) in athyreotic patients after total thyroidectomy may appear straightforward to manage. However, robust evidence to guide therapy remains lacking. This study aimed to provide further information on the efficacy of fixed, weight-adjusted LT4 dosing initiated immediately after surgery. Materials: Consecutive patients were enrolled at a single institution applying a standardized postoperative protocol: all cases initiated LT4 therapy immediately postoperatively at dose of ~1.6 mcg/kg, undergo their thyroid function test after six weeks, and receive subsequent dose adjustments until the target is reached. Results: Forty-eight patients met the inclusion criteria. The median LT4 starting dose was 100 mcg per day and 1.56 mcg/kg of body weight per day. At the first follow-up, 16 (33.3%) patients were at target. Over follow-up, the overall median time-to-target was 4 months. The 32 patients who reached the target later included 15 patients showing a decreased LT4 requirement and 17 patients with an increased LT4 need. The correlation analysis between body weight and LT4 dose revealed significant negative association between LT4 dose and weight variation (R² 0.18). In the multiple linear regression body weight and comorbidities were positively associated with LT4 dose on target, while age showed a negative association. Conclusions: Early postoperative weight changes influence significantly LT4 dose requirements, and age and comorbidities provided additional predictive value. These findings highlight the need for early follow-up and LT4 titration in patients not at target after initial evaluation.