Endocrine Abstracts

Introduction

There is no consensus about biological targets in patients with central hypothyroidism (CH). The main objective of this work was to characterize our patients with CH.

Design

We conducted a retrospective study at the University Hospital of Amiens. In our center, patients with CH are considered “well substituted” if the free thyroxine (FT4) is in the upper half of the reference interval and the free triiodothyronine (FT3) within the normal range. We studied the FT4/FT3 ratio in all and “well-substituted” patients and the determinants of FT4/FT3 in patients with normal FT3.

Results

124 patients were included between 01/07/2016 and 31/07/2018. CH was due to pituitary adenoma in 100 patients. The average dose-weight of levothyroxine was 1.34 µg/kg/day. The average FT4/FT3 ratio was 4.04 with a a physiological ratio (3.10–3.30) in only10 patients. 36% of the patients were considered “well substituted”. They had a significantly higher TeBG (P = 0.028) and lower triglycerides (P = 0.044) ; the ratio was physiological in only 2 patients and ratio was higher in women than men: 4.54 vs 3.94 (P = 0.034). 101 of all patients had FT3 within the normal range. FT3 was significantly lower in obese patients (P <0.01). Patients with FT3 higher than the calculated median had a FT4/FT3 ratio closer to the physiological ratio.

Conclusion

Treatment of CH remains a challenge for the endocrinologist. It seems relevant to target a FT3 close or higher than the median, without considering the FT4 to obtain aphysiological FT4/FT3 ratio but the obtention of a clinical improvement has to be evaluated.

Key-words

central hypothyroidism, levothyroxine, free thyroxine, free triiodothyronine, FT4/FT3 ratio