459 adult patients who received a hemithyroidectomy at the Department of General Surgery, Division of Endocrine Surgery and a follow-up visit (3-12 months post-surgery) at the thyroid outpatient clinic of the Department of Endocrinology and Metabolism, Medical University of Vienna between 1994 and 2018 were identified and investigated in this retrospective study. The aim of this study was to investigate whether patients post right side hemithyroidectomy require a higher mean levothyroxine dosage than patients after left lobe hemithyroidectomy as the right thyroid lobe is bigger than the left lobe. Further, we aimed at developing a better post-surgery thyroid dosage prediction model.

In most patients, the right lobe of the thyroid gland is larger than the left lobe. After a hemithyroidectomy, the remaining lobe grows by up to 30% to compensate for the loss. However, thyroxine replacement is still necessary for 22% to 60% of all patients. The aim of this study is to investigate whether a right-lobe hemithyroidectomy predisposes to a higher postoperative dose of levothyroxine.

Patients and Methods In a retrospective cohort study, 459 patients over the age of 18 years who underwent a hemithyroidectomy at the Department of General Surgery, Division of Endocrine Surgery and a follow-up (3-12 months post-surgery) visit at the thyroid outpatient clinic of the Department of Endocrinology and Metabolism between 1994 and 2018 were investigated. The study was approved by the local ethics committee and performed in accordance with the Declaration of Helsinki. The work has been reported in line with the STROCSS criteria. The patients were identified via data extraction from a university hospital-wide Research, Documentation and Analysis (RDA) database. In a second step, further information necessary for the analysis (ultrasound data on pre-surgery thyroid volume, pre-surgery TSH, side and date of hemithyroidectomy, surgery protocol, underlying thyroid disease, type and dosage of treatment, age, weight, height, thyrotropin (TSH), free T4 (fT4), free T3 (fT3)) were extracted from the internal electronic health record system. Patients who had either received radiation therapy had undergone previous thyroid surgery, surgery on the contralateral lobe, had pre-existing hypothyroidism, an autoimmune disease of the thyroid or were pregnant were excluded from the analysis. 33 patients were excluded due to additional surgery on the contralateral lobe resulting in a total of 426 patients. Pre-surgery ultrasound thyroid volume was calculated with the volumetric ellipsoid method (height × width × depth × correction factor 0.524).

Inclusion Criteria:

• 18 years
• Males and females
• St.p. hemithyroidectomy

Exclusion Criteria:

• Radiation therapy
• Pregnancy
• Previous thyroid surgery (e.g. nodule removal surgery)

All patients who received a hemithyroidectomy at the Department of General Surgery, Division of Endocrine Surgery and a follow-up visit (3-12 months post-surgery) at the thyroid outpatient clinic of the Department of Endocrinology and Metabolism, Medical University of Vienna between 1994 and 2018 were identified and investigated in this retrospective study.