BMI Helps to Calculate the Initial Levothyroxine Dose After Total Thyroidectomy

Abstract

Abstract After total thyroidectomy, an initial dose of levothyroxine is often prescribed based on the patient’s body weight (1.6 mcg / kg / day), regardless of body mass index (BMI). The current literature required that hormone maintenance therapy (THR) in obese patients differs from non-obese patients. Review of the clinical processes of patients with papillary carcinoma followed in the multidisciplinary consultation of Endocrine Pathology at CHVNG / E followed a total thyroidectomy from 2015 to 2017. Patients who achieved euthyroidism with THR were included in the analysis and divided according with BMI. Statistical analysis was performed using SPSS version 25.0. A value of p <0.05 was considered statistically significant. The sample included 82 patients, 90.2% (n = 74) female and 9.8% (n = 8) male, with an average age of 53.02 ± 14.27 years. Of the female gender, 52.4% (n = 43) were in menopause. In the postoperative period, 14 patients (17.1%) had a normal BMI, 46 (50%) were overweight and 22 (32.9%) were obese. The average follow-up time was 75.3 months (32-128). A dose of LT4 required to achieve euthyroidism based on the BMI categories mentioned above was 1.70; 1.54 and 1.49 mcg / kg. Patients with a higher BMI needed a higher dose of LT4 to achieve euthyroidism (p <0.05), but the dose was lower in relation to weight (mcg / kg) (p <0.05). There were no differences related to age and need for L-T4 suplementation (p> 0.05). Our study shows that de calculation of the initial levothyroxine dose should also take into account BMI. Overweight and obese individuals should receive a lower dose than that used in normal weight patients, which goes against what has been described in the literature. The weight-based formula, unlike BMI, does not account for the volume of distribution of L-T4 well. Other methods, which include, for example, ideal body weight instead of actual weight, are being developed to help choose the starting levothyroxine dose.