Long-term Effect of Bariatric Surgery on the Use of Levothyroxine and Thyroid Levels

BACKGROUND: The aim of this study was to evaluate the effect of bariatric surgery on the defined daily dose of levothyroxine (DDD LT4), thyroid-stimulating hormone (TSH), and free thyroxine (fT4) in female patients with hypothyroidism until 48 months after surgery.METHODS: A retrospective observational study of hypothyroid patients who underwent bariatric surgery. Changes in DDD LT4, TSH, and fT4 over a 48 month period after surgery were analyzed.RESULTS: Thirty-seven patients were included: 27 Roux-en-Y gastric bypass (RYGB), 6 sleeve gastrectomy (SG), 3 adjustable gastric band, and 1 one anastomosis gastric bypass. The median DDD LT4 decreased from 125 µg at baseline to 100 µg 12 months after surgery. From 24 to 48 months after surgery, the median DDD LT4 was stable at 125 µg. Most dose adjustments occurred during the first 24 months after surgery. In the time period of 24-48 months after surgery, the dose remained stable in 73.1% of the RYGB patients and in 60.0% of the SG patients. After 48 months in the RYGB group, no significant change in TSH and fT4 levels was observed.CONCLUSIONS: Bariatric surgery led to frequent dose adjustments during the first 2 years after surgery. However, 24-48 months after surgery in the majority of patients, the dosage remained stable. No significant change in TSH and fT4 was observed 48 months after RYGB. In the first 2 years after surgery, clinicians should frequently monitor TSH and fT4 for individual dose adjustment of levothyroxine. Thereafter, the frequency of monitoring may be decreased.