Comparison of Dosing Schemes for Thyroid Hormone Replacement Therapy After Thyroidectomy

Area of Science:

• Endocrinology
• Pharmacology
• Clinical Medicine

Background:

• Current thyroid hormone replacement therapy (THRT) dosing relies on weight-based calculations.
• A novel Poisson regression model incorporating seven clinical variables was proposed to enhance THRT accuracy.
• This study compares the accuracy of a novel Poisson model (Scheme A) against the standard weight-based method (Scheme B) for THRT dose estimation post-thyroidectomy.

Purpose of the Study:

• To compare the accuracy of estimated THRT dose to achieve a euthyroid state between a novel Poisson regression model (Scheme A) and the standard weight-based method (Scheme B).
• To evaluate the difference in predicted THRT dose between the two schemes.
• To assess dosing error rates, particularly overdosing and underdosing, in patients undergoing total thyroidectomy for benign conditions.

Main Methods:

• Retrospective review of 406 patients who underwent total thyroidectomy for benign disease (2011-2019).
• THRT dose calculated using both Scheme A (Poisson model) and Scheme B (weight-based).
• Comparison of prediction rates for optimal THRT dosing, achievement of euthyroid state (TSH 0.45-4.5 mIU/L), and dosing error rates (> 25 mcg over/underdosing).

Main Results:

• Scheme A showed lower overdosing errors (17.9% vs. 32.1%, P=0.0025) and a trend towards less extreme overdosing (17.9% vs. 26.1%, P=0.08) compared to Scheme B.
• Scheme A demonstrated significantly lower overdosing in obese patients (19.2% vs. 45.2%, P=0.0006).
• The average predicted dose difference between schemes was approximately 16 µg, and agreement was low to moderate (Kappa=0.360) in patients achieving euthyroid state.

Conclusions:

• The Poisson regression model (Scheme A) resulted in lower overdosing rates, particularly in obese patients, compared to the weight-based method (Scheme B).
• While no statistically significant difference in overall accuracy was found, the reduction in overdosing errors suggests clinical relevance.
• Incorporating clinical variables beyond weight may be crucial for optimizing THRT, especially in patients with higher BMIs.