Levothyroxine dosage determination according to Body Mass Index (BMI) after total thyroidectomy

Abstract

Objective: Currently, postoperative thyroid hormone replacement dosing is weight-based with adjustments and made following Thyroid Stimulating Hormone (TSH) values, which may lead to delayed achievement of euthyroidism and failure in achieving an accurate estimation of the levothyroxine dose. We aimed to evaluate the relationship between Body Mass Index (BMI) and Lean Body Mass (LBM) with levothyroxine dose. Materials and Methods: Eighty patients with thyroid disease (benign and malignant) randomly enrolled the study. BMI and LBM were calculated during the pre-operative visit. Thyroid hormone replacement was started five day after surgery for benign and after a month for malignant cases, at a dose of 1.6 mcg/kg/day based on actual body weight. When euthyroidism was achieved, the levothyroxine dose was measured, and efforts were made to analyze its relationship with weight, BMI, and LBM. Results: In the benign group, levothyroxine dose was obtained at 1.51 mcg/kg per body weight. To determine the levothyroxine dose based on BMI and LBM, Y=-0.013+0.005 BMI and Y=0.048+0.002 LBM formulas were used, respectively. In the malignant group, a levothyroxine dose of 1.56 mcg/kg was obtained based on the weight variable. To determine the levothyroxine dose based on BMI and LBM, Y=0.01+0.004 BMI and Y=0.042+0.002 LBM formulas were used, respectively. In both groups, the levothyroxine dose that was calculated was more accurate using BMI with the obtained formula. Conclusion: Weight, BMI, and LBM can be used to determine the levothyroxine dose in patients receiving total thyroidectomy, but levothyroxine can be precisely measured using BMI.

Levothyroxine Therapy Adequacy, Dose Estimation and Vitamin D Effect Assessment in a Sample of Iraqi Female Patients with Different Causes of Hypothyroidism

“…Maghsudi et al compared the efficacy of actual weight, LBM, and BMI based dosing and concluded that BMI had the strongest correlation with LT4 dose and derived a dose calculation formula: Y= -0.013 +0.005 BMI for benign pathology in total thyroidectomy patients (24) . On the other hand, Al-Dhahari et al (25) identified Body Surface Area (BSA) as the most significant predictor and proposed a model accordingly.…”

Lipid Profile Change after Thyroidectomy

“…Moreover, TSH levels are increased in patients with obesity, an effect that can be attributed to the leptin hormone produced by adipose tissue. The secretion of T4 and T3 and metabolism of T4 to T3 decreases in healthy elderly patients, although the levels of rT3 increase; the half-life for elimination of T4 can be checked for longer duration (19,20).…”

The clinical effects of fine-tuning: Thyroid hormone replacement

“…Toomatari et al investigated the relationship between body weight, BMI, LBM, and the dose of Lthyroxine in patient groups that had undergone total thyroidectomy for benign and malignant thyroid conditions. The authors concluded that BMI is the most favorable parameter, and they also presented new equations for predicting the accurate L-thyroxine dose based on weight, BMI, and LBM (8).…”