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

Abstract

Background The 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. Objectives To determine the weight and BMI-based dosing of thyroxine in primary hypothyroidism to achieve euthyroidism. Material and methods It 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. Results The mean age was 443 +/- 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