Median-lower normal levels of serum thyroxine are associated with low  triiodothyronine levels and body temperature in patients with central  hypothyroidism

Hirata Y, Fukuoka H, Iguchi G, Iwahashi Y, Fujita Y, Hari Y, Iga M, Nakajima S, Nishimoto Y, Mukai M, Hirota Y, Sakaguchi K, Ogawa W, Takahashi Y

doi:10.1530/EJE-15-0130

Median-lower normal levels of serum thyroxine are associated with low triiodothyronine levels and body temperature in patients with central hypothyroidism

Hirata Y et al., 2015

European Journal of Endocrinology, 173(2), 247-256

DOI 10.1530/EJE-15-0130 PMID 25994949

Abstract

Objective

Although it has been recommended that serum free thyroxine (FT4) levels should be targeted to middle-upper normal levels during levothyroxine (l-T4) replacement therapy in patients with central hypothyroidism (CeH), the rationale has not been clarified.

Methods

A retrospective single-center study enrolled 116 patients with hypothyroidism (CeH, n=32; total thyroidectomy (Tx), n=22; primary hypothyroidism (PH), n=33; and control benign thyroid nodule (C), n=29). The patients had received L-T4 therapy at the Kobe University Hospital between 2003 and 2013. They were stratified according to serum FT4 level (≥ 1.10 or <1.10 ng/dl), and body temperature (BT), serum free triiodothyronine (FT3) levels, FT3/FT4 ratio, and lipid profiles were compared. The effect of GH replacement therapy on thyroid function was also analyzed.

Results

FT3 levels and FT3/FT4 ratios were significantly lower in patients with CeH than in patients with PH (P<0.05) or C (P<0.05). In patients with FT4 <1.10 ng/dl, BT was significantly lower in patients with CeH (P=0.002) and Tx (P=0.005) than in patients with PH, whereas no differences were found in patients with FT4 ≥ 1.10 ng/dl. In patients with CeH, FT3 levels were higher in those with GH replacement therapy (P=0.018).

Conclusion

In CeH, patients with median-lower normal levels of serum FT4 exhibited lower serum FT3 levels and lower BT. These results support the target levels of serum FT4 as middle-upper normal levels during l-T4 replacement therapy in patients with CeH.

Topics

General OB/GYN > Thyroid Disorders > Central Hypothyroidism Reproductive Endocrinology > Thyroid Function > Levothyroxine Replacement Diagnostics > Hormone Testing > Thyroid Hormone Levels

central hypothyroidism levothyroxine replacement FT4 target levels, free thyroxine free triiodothyronine ratio central hypothyroidism, low body temperature hypothyroidism thyroid hormone replacement, FT3 FT4 ratio central vs primary hypothyroidism, GH replacement therapy effect on thyroid function, median lower normal FT4 levels clinical significance, T4 to T3 conversion central hypothyroidism retrospective study, serum thyroxine target middle upper normal levothyroxine therapy, thyroidectomy vs central hypothyroidism body temperature differences, growth hormone deficiency thyroid function interaction

PMID 25994949 25994949 DOI 10.1530/EJE-15-0130 10.1530/EJE-15-0130

Cite this article

Hirata, Y., Fukuoka, H., Iguchi, G., Iwahashi, Y., Fujita, Y., Hari, Y., Iga, M., Nakajima, S., Nishimoto, Y., Mukai, M., Hirota, Y., Sakaguchi, K., Ogawa, W., & Takahashi, Y. (2015). Median-lower normal levels of serum thyroxine are associated with low triiodothyronine levels and body temperature in patients with central hypothyroidism. *European journal of endocrinology*, *173*(2), 247-256. https://doi.org/10.1530/EJE-15-0130

Keywords

Biomarkers, Triiodothyronine, Thyroxine