Patients require roughly 13% more levothyroxine substitution after hemithyroidectomy of the right lobe compared to the left lobe, which should be considered in post-op care.
Key Findings
Results
Patients who underwent right-lobe hemithyroidectomy required a significantly higher mean levothyroxine dosage than those who underwent left-lobe hemithyroidectomy.
Mean levothyroxine dosage after right-lobe hemithyroidectomy was 68.1 µg/day compared to 60.2 µg/day after left-lobe hemithyroidectomy.
The difference was statistically significant (p = 0.018).
This represents approximately 13% more levothyroxine substitution after right-lobe compared to left-lobe hemithyroidectomy.
The analysis used a weight and pre-surgery TSH-adjusted model.
Background
A substantial proportion of patients still require thyroxine replacement after hemithyroidectomy.
Between 22% and 60% of all patients require thyroxine replacement post-hemithyroidectomy.
This range is cited from existing literature as context for the study.
The remaining lobe grows by up to 30% as compensation after hemithyroidectomy.
Methods
The study population consisted of 426 adult patients who received hemithyroidectomy and follow-up at the Medical University of Vienna.
426 adult patients were identified and investigated in this retrospective study.
Patients were treated at the Medical University of Vienna between 1994 and 2018.
Median follow-up visit occurred 9 months post-surgery.
The study design was retrospective.
Background
The right lobe of the thyroid gland is typically larger than the left lobe, providing a biological rationale for the dosage difference.
The right lobe being larger than the left lobe is cited as the usual anatomical finding.
Removal of the larger right lobe would leave less functional thyroid tissue, explaining the greater need for levothyroxine replacement.
This anatomical difference is presented as the mechanistic basis for the study hypothesis.
What This Means
This research suggests that the side of the thyroid gland removed during a partial thyroid surgery (hemithyroidectomy) matters when determining how much thyroid hormone medication a patient will need afterward. Specifically, patients who had their right thyroid lobe removed needed about 13% more levothyroxine (a synthetic thyroid hormone) per day on average — about 68 µg/day — compared to patients who had their left lobe removed, who needed about 60 µg/day. This difference was statistically meaningful and held up even after accounting for patients' body weight and pre-surgery thyroid hormone levels.
The likely explanation is anatomical: the right thyroid lobe is generally larger than the left. When the right lobe is removed, the remaining left lobe is smaller and produces less thyroid hormone on its own, even accounting for the compensatory growth of up to 30% that the remaining lobe typically undergoes after surgery. Between 22% and 60% of patients who have a hemithyroidectomy end up needing thyroid hormone replacement therapy at all, and this study adds nuance by showing that the required dose is not the same for everyone.
This research suggests that doctors managing patients after partial thyroid surgery should consider which lobe was removed when determining the starting dose of levothyroxine. Patients who had their right lobe removed may need a higher initial dose than those who had their left lobe removed, potentially leading to faster achievement of stable thyroid hormone levels and avoiding the complications of hypothyroidism in the post-operative period.
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Deischinger C, Krebs M, Scherer T, Scheuba C, Kautzky-Willer A, Kosi-Trebotic L. (2026). Higher Post-Operative L-Thyroxine Dosage Needed After Right Compared to Left-Lobe Hemithyroidectomy.. Endocrinology, diabetes & metabolism. https://doi.org/10.1002/edm2.70345