Levothyroxine dosing post total thyroidectomy – the ideal equation?

Abstract Aims Levothyroxine (LT4) therapy is necessary post total thyroidectomy to suppress TSH for differentiated thyroid cancer (DTC) and euthyroidism benign disorders. We aim evaluate the accuracy of empirical LT4 regimens alongside existing formulas in literature identify predictive variables dosage. Methods Retrospective study between January 2018 February 2021 all thyroidectomies at UHNM. Total 50 cases identified from central database each group (DTC vs benign). Data collected analysed including patient demographics, diagnosis, function. Results Most patients were started empirically on 125mcg/day (92% 90%, DTC This led 78% 82% being within 25mcg final regimen. For thyroidectomies, comparing versus recommended 2mcg/kg had an average error -9.1% +26.1%. Correlation Body Mass Index (BMI), Lean (LBM) or Surface Area (BSA) was weak moderate (r=0.4 p=0.002, r=0.6 p=<0.001, p=<0.001). BNF dose 1.6mcg/kg resulted ranging -1.9% +27.1%. The best +0.2% using formula 1.5mcg/kg by Jin et al. No correlation found BMI, LBM BSA with (r=0.1 p=0.443, r=0.2 p=0.216, p=0.211). Conclusion In our subset, dosing 125mcg gives reasonable estimate dose. alone not a consistent predictor Further validation needed.