Weight and Body Mass Index for Predicting Thyroxine Dose in Primary Hypothyroidism

Abstract

BackgroundThe treatment of primary hypothyroidism with thyroxine is weight-based or body mass index (BMI)-based. However, significant variation in the dose and the consequent delay in achieving euthyroid state is observed along the spectrum of patient body weights. ObjectivesTo determine the weight and BMI-based dosing of thyroxine in primary hypothyroidism to achieve euthyroidism. Material and methodsIt was a retrospective review of the patient records conducted in the department of endocrinology, Shifa International Hospital, Islamabad, from July 1, 2014, to June 30, 2019 (five-year period). Patients with clinical and biochemical hypothyroidism were enrolled and initiated on thyroxine replacement to achieve euthyroid status. A total of 504 patients were included in the study. ResultsThe mean age was 44.5 ±13.6 standard deviation. Females were 83.5%. The mean dose of thyroxine to achieve euthyroid status was 107.7 ± 39.3 mean standard deviation mcg/day, i.e. 1.4 (0.5) mcg/kg/day. Euthyroid status was achieved in 264 (52.4%) of patients at three months. The mean TSH level after treatment was 2.09 (1.2) mU/L. The linear regression model showed that BMI and weight are independent predictors of the required thyroxine dose (R and R square values are .274 and 0.075 for BMI and .319 and .102 for weight, respectively (P-value <.0001). There was no impact of age, gender, height, and duration of disease on achieving euthyroid at six months after treatment (P values: .85, .394, .827, and .105, respectively). ConclusionThe optimum dose in primary hyperthyroidism can be determined with body weight and BMI-based calculations.

Real-world derived weight-based levothyroxine doses to achieve optimal thyrotropin target in different degrees of autoimmune hypothyroidism

“…In another retrospective study of 504 patients with hypothyroidism, there was a significant decrease in weight-based L-T4 dose with increasing actual body weight categories [14]. In the present study, body weight categories may further guide weight-based L-T4 dosing…”

“…Weight-based L-T4 doses in group 1 were 1. 14 and (1.03 ± 0.21 µg/kg/day) for body weight subcategories < 70 kg, 70-100 kg, and > 100 kg, respectively [p = 0.004] (Table 4).…”

“…Similarly, Southeast Asians seem to have lower L-T4 requirements to achieve euthyroidism compared to those recommended by the ATA. In two studies, one from Pakistan and the other from Singapore-including patients with a diagnosis of primary hypothyroidism-L-T4 requirements to achieve euthyroidism were 1.4 and 1.1 µg/kg/day respectively [9,14]. Environmental and racial differences may account for different requirements.…”

Refractory Hypothyroidism: Unraveling the Complexities of Diagnosis and Management

“…40 The appropriate dosage of LT4 is typically determined based on residual thyroid function, target TSH levels, patient weight, and BMI. 96 Determining the optimal dosage for individuals with obesity is challenging, involving considerations of body weight, ideal weight, and lean body mass. 97 Lean body mass is a key predictor of LT4 requirements due to its role in T4 metabolic processes.…”