Work

Lean Body Mass as a Predictor of Levothyroxine Requirement in Primary Hypothyroidism as Compared to Actual Body Weight

Year: 2025

Type: article

Abstract: Context Levothyroxine (LT4) therapy for hypothyroidism is traditionally dosed at 1.6 μg/kg of actual body weight (ABW). However, ABW-based dosing often fails to proportionally adjust for increasing body weight. Ideal body weight (IBW) and lean body mass (LBM) have been proposed as alternatives, but data on these parameters on the larger hypothyroid population are lacking, particularly in Hashimoto thyroiditis. Objective This study evaluates LBM- and IBW-based LT4 dosing and examines variability in ABW-based dosing across age, body mass index (BMI), and menopausal status. Methods This cross-sectional study analyzed 720 patients with primary hypothyroidism on stable LT4 doses and in a euthyroid state for ≥6 months. ABW, BMI, LT4 dose, and thyrotropin (TSH) were recorded. IBW and LBM were calculated using Devine's and Boer's formulas, respectively. LT4 doses per ABW, IBW, and LBM were compared across age, BMI, and menopause. Results Daily LT4 dose per kilogram of ABW decreased across BMI categories (18.5-24.9 kg/m2: 1.73 ± 0.34 µg/kg, 25-29.9 kg/m2: 1.51 ± 0.30 µg/kg, ≥ 30 kg/m2: 1.33 ± 0.31 µg/kg; P < .001). In contrast, IBW-based dosing increased with BMI (1.92 ± 0.40, 2.09 ± 0.47, 2.25 ± 0.51 µg/kg respectively; P < .001), while LBM-based dosing remained consistent (2.37 ± 0.48, 2.37 ± 0.52, 2.35 ± 0.54 µg/kg respectively; P = .91). LT4 dose decreased significantly with age (P < .001) in ABW-based dosing but showed no significant change with LBM (P = .224) or IBW (P = .377). ABW-based dosing was significantly lower in postmenopausal patients (P < .001), while IBW and LBM-based dosing showed no significant variation. Conclusion LT4 dosing based on LBM offers a more consistent approach for managing hypothyroidism. A dose of 2.3 mcg/kg LBM may optimize treatment outcomes.

Source: Journal of the Endocrine Society

DOI: 10.1210/jendso/bvaf159

Authors: Damacharlla Venkateswarlu, Manjunath Goroshi, Vanishri Ganakumar, Vikrant Ghatnatti, Sruthi Kotla

Institutions: Jawaharlal Nehru Medical College, KLE Academy of Higher Education and Research

Language: English

Topic: Thyroid Disorders and Treatments

Subfield: Endocrinology, Diabetes and Metabolism

Field: Medicine

Domain: Health Sciences

SDG: Good health and well-being

Open Access status: gold

Estimated APC paid: $3,255