Evaluation of Thyroid Hormone Replacement Dosing in Overweight and Obese Patients After a Thyroidectomy

Initiation of thyroid hormone replacement (THR) after a total thyroidectomy has traditionally relied on the weight of the patient, regardless of the patient's body mass index (BMI). Current literature suggests that THR in obese patients differs from nonobese patients. This can lead to overdosing of levothyroxine (LT4) and delay in achievement of euthyroid state. We retrospectively identified patients on THR after total thyroidectomy with a benign postoperative diagnosis. Patients who achieved euthyroidism with THR were included in the analysis. Patient demographic and THR dosing information was collected. Regression analysis was performed to identify appropriate THR dosing at varying BMIs. This study aimed to evaluate the appropriate dosing of THR in overweight and obese patients. Our cohort consisted of 114 patients achieving euthyroidism while on THR. Mean age was 55 years (range 28-77 years) with 84% females. Of the 114 patients, the number of patients with a BMI less than 25, 25-29, 30-34, 35-39, and greater than 40 were 26 (23%), 33 (29%), 23 (20%), 19 (17%), and 13 (11%), respectively. Of the entire cohort, a mean of 50 weeks elapsed after surgery to achieve euthyroidism, with no significant difference between the BMI categories (p = 0.58). In obese patients (BMI >30), 35% were overdosed with LT4 on initial dosing. The cohort lost a mean of 3 kg until euthyroidism was achieved, with no significant difference in the weight loss based on BMI category (p = 0.61). Patients with a higher BMI did require a higher dose (mcg) of LT4 to achieve euthyroidism (p < 0.01), but the dose was significantly lower in relation to their weight (mcg/kg) (p < 0.01). The LT4 dose required to achieve euthyroidism based on the previously mentioned BMI categories were 1.76, 1.47, 1.42, 1.27, and 1.28 mcg/kg. The current weight-based dosing of THR inappropriately overdoses overweight and obese patients. A more appropriate formula for THR titration should consider both the weight and BMI of the patient.