Endocrine Abstracts

Introduction: The long-term follow-up of the patients with well-differentiated thyroid cancer (WDTC) includes the monitoring of suppressive levothyroxine therapy. Our study evaluated the peculiarities of thyroid status in WDTC patients on the doses of levothyroxine leading to TSH suppression (lower than 0.5 mI/l).

Study design: We have studied 114 patients with WDTC, 24 men and 90 women. The follow-up was a least 10 years after thyroid surgery, mean age at the study was 28.42±0.29 years. The mean daily levothyroxine dose was 2.65±0.05 μg/kg. The control group presented with age and sex-matched healthy subjects. The estimation of thyroid function tests was done using ELISA-kits (DRG, USA).

Results: In WDTC patients, 24 h after the last levotyroxine dose, the mean TT₄ and FT₄ levels were 30 and 20% higher compared to the control; FT₃ levels did not differ. The most frequent hormonal changes were as follows: TT₄ elevations – 46.5%, FT₄ – 18.4%, and FT₃ – 10.5%. An elevated T₄ was more frequent in female patients compared to male ones (51.5 vs 29.2%). On the contrary, FT₃ elevation was detected more often in man than in woman (20.8 vs 7.8% respectively). In the subset of patients with an increased FT₃, the statistically lower total cholesterol level was revealed compared to the patients with normal levels of the thyroid hormones; however, the mean levothyroxine doses did not differ significantly in two subgroups.

Conclusion: A proportion of WDTC patients–who receive 2.65±0.05 μg/kg of levothyroxine and have TSH suppression lower than 0.5 mI/l–simultaneously have an elevated FT₃ levels. Such patients may have a higher individual sensitivity to thyroid hormone’s action and need an individual dose correction during their monitoring to provide an optimal hormonal and metabolic control.