Evaluation of Thyroid Hormone Replacement Dosing in Morbidly Obese Hypothyroid Patients after Bariatric Surgery-Induced Weight Loss

Abstract

The most frequent endocrine disease in obese patients is hypothyroidism. To date, there are no clear data regarding what happens to the dose of levothyroxine (LT4) after bariatric surgery (BS). The objective of the present study was to evaluate thyroid hormone replacement dose in morbidly obese hypothyroid patients after BS-induced weight loss. We explore the best type of measured or estimated body weight for LT4 dosing. We performed an observational study evaluating patients with morbid obesity and hypothyroidism who underwent BS. We included 48 patients (three men). In morbidly obese hypothyroid patients 12 months after BS-induced weight loss, the total LT4 dose or the LT4 dose/kg ideal body weight did not change, while there was a significant increase in LT4 dose/body surface area, LT4 dose/kg weight, LT4 dose/kg adjusted body weight, LT4 dose/kg body fat, and LT4 dose/kg lean body weight. There were no differences in LT4 dose and its variation between sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB). The present study strongly suggests that LT4 dosing in obese hypothyroid patients can be individually adapted more precisely if it is based on ideal body weight.

Thyroid Function Alteration in Obesity and the Effect of Bariatric Surgery

“…These result highly suggest that sleeve gastrectomy and a Roux-en-Y Gastric Bypass showed different changes in levothyroxine needs. However, in agreement with Pedro et al [ 77 ], our group study did not find the bariatric surgery technique to be a predictor of levothyroxine dose variation [ 94 ]. Similar results have been found by other authors; both sleeve gastrectomy and a Roux-en-Y Gastric Bypass improved thyroid function in the same way [ 90 ].…”

“…Other authors have found similar results with a decrease or no change in the total levothyroxine requirement, but an increase of the weight-based levothyroxine requirement after bariatric surgery [ 93 ]. Our group has encountered that, following bariatric surgery, the total levothyroxine or the levothyroxine dose/kg of IBW did not change; however, the levothyroxine dose/body surface area, levothyroxine dose/kg of actual BW, levothyroxine dose/kg of adjusted BW and levothyroxine dose/kg of LBW increased [ 94 ].…”

“…In summary, in most of the studies, weight loss following bariatric surgery provokes a diminution in total levothyroxine needs. Juiz-Valiña et al have found that in obese hypothyroid patients treated with BS, the absolute levothyroxine dose did not change, nor did the levothyroxine dose/kg of IBW, but the levothyroxine dose/body surface area, levothyroxine dose/kg of actual BW, or levothyroxine dose/kg of LBW significantly increased [ 94 ]. A change in the absolute levothyroxine dose and levothyroxine dose/kg of IBW was not related to excessive weight loss.…”

“…A change in the absolute levothyroxine dose and levothyroxine dose/kg of IBW was not related to excessive weight loss. On the contrary, excessive weight loss was related to an increase in the levothyroxine dose/body surface area, and levothyroxine dose/kg of present BW [ 94 ]. These data suggest that the thyroid hormone replacement change after bariatric surgery is due to a mixed mechanism, a decrease in levothyroxine needs due to weight loss and a decrease in levothyroxine absorption due to the surgical procedure.…”

“…Furthermore, in a multivariable analyses study, the levothyroxine dose was predicted by the amount of fat-free mass, hypothyroidism etiology, and the sex of the patients [ 102 ]. Juiz-Valiña et al observed that in extreme obese patients, after bariatric surgery the levothyroxine dose/kg of IBW did not change, however, the levothyroxine dose/body surface area, levothyroxine dose/kg of actual BW, or levothyroxine dose/kg of lean BW increased [ 94 ]. In summary, thyroid hormone replacement titration in hypothyroid patients with excessive adiposity can be adjusted more correctly based on IBW.…”