Thyroid Hormone Replacement Dosing after Bariatric Surgery in Patients with Primary Hypothyroidism And Severe Obesity: Tehran Obesity Treatment Study.

TSH levels decreased over time in the sleeve gastrectomy group but did not significantly change in the OAGB group during follow-up.

• TSH and T4 measurements did not significantly change in the OAGB group over the 36-month follow-up period.
• In the SG group, TSH measurement decreased over time with ptrend <0.001.
• The study followed 1030 patients with hypothyroidism for 36 months post-surgery.
• SG group comprised 707 patients (88.3% women) and OAGB group comprised 323 patients (92% women).

The majority of patients in both surgical groups experienced LT4 dose reduction or no change by the third year of follow-up.

• In the third year, 56.1% of SG patients and 33.3% of OAGB patients experienced LT4 dose reduction.
• 24.4% of SG patients and 9.1% of OAGB patients experienced LT4 dose increments in the third year.
• LT4 dose was measured in μg/day.
• These findings suggest that most hypothyroid patients undergoing bariatric surgery do not require increased LT4 dosage over time.

The LT4/fat mass ratio increased significantly after 36 months of follow-up in both the SG and OAGB groups.

• In the SG group, LT4/FM (μg/kg) ratio increased from 1.8 (1.5–2.2) at baseline to 2.7 (2.0–3.5) at 36 months (ptrend = 0.039).
• In the OAGB group, LT4/FM (μg/kg) ratio increased from 1.7 (1.4–2.2) at baseline to 3.2 (2.7–4.8) at 36 months (ptrend <0.001).
• GEE analysis adjusted for weight as a time-varying covariate was used to assess LT4 requirements.
• The increase in LT4/FM ratio plateaued after the first year in both groups (pinteraction = 0.009).

Patients who underwent OAGB experienced greater LT4/fat mass dose adjustments compared to those undergoing SG.

• The difference in LT4/FM (μg/kg) adjustments between OAGB and SG groups approached but did not reach conventional statistical significance (pbetween = 0.060).
• The OAGB group showed a larger absolute increase in the LT4/FM ratio (from 1.7 to 3.2 μg/kg) compared to the SG group (from 1.8 to 2.7 μg/kg).
• Both surgical groups showed a plateau in LT4/FM increase after the first postoperative year.
• OAGB is a procedure involving both restrictive and malabsorptive components, which may account for greater LT4 dose-per-fat-mass adjustments.

The study was designed as a three-year prospective cohort study using bioelectrical impedance analysis for body composition assessment and GEE methods for LT4 requirement analysis.

• 1030 patients with hypothyroidism were included, undergoing either SG (n=707) or OAGB (n=323).
• Body composition was assessed using a bioelectrical impedance analyzer.
• LT4 requirements were assessed by generalized estimating equation (GEE) methods adjusted for weight as a time-varying covariate.
• Patients were followed for 36 months after surgery with serial TSH, T4, and LT4 dose measurements.

Obesity and hypothyroidism are described as commonly associated medical conditions, and bariatric surgery is noted as a common approach for substantial weight loss in obese patients.

• The authors note there is limited evidence regarding the need for post-surgery LT4 dose adjustment in patients with hypothyroidism undergoing bariatric surgery.
• The study was motivated by the gap in knowledge about how BS affects LT4 requirements with attention to body composition changes.
• Both SG and OAGB were examined to compare the effects of two different bariatric procedures on thyroid hormone replacement dosing.