ESPE Abstracts (2014) 82 P-D-3-1-979

Free T3/free T4 Ratios in Children with Hypothyroidism Treated with Levothyroxine Monotherapy

Tsutomu Takahashi, Yuki Konno & Ikuko Takahashi

Akita University Graduate School of Medicine, Akita-shi, Japan

Background: Levothyroxine monotherapy is the treatment of choice for congenital hypothyroidism (CH). Recently, it was reported that levothyroxine monotherapy cannot guarantee euthyroidism in all athyreotic adult patients. A more physiological treatment than levothyroxine monotherapy was suggested to be required in some patients with hypothyroidism.

Objective and hypotheses: To elucidate whether levothyroxine monotherapy is appropriate for all children with hypothyroidism. Levothyroxine monotherapy may not sustain physiological condition of thyroid hormones in some children with hypothyroidism.

Method: Serum thyroid hormones, free T3 (pg/ml), free T4 (pmol/l), TSH (mU/l), and free T3:free T4 ratio (pg/ml per pmol/l), were determined in a control group (n=54), a severe CH group (n=5), a mild CH group (n=18), and a pan-hypopituitarism (PHP) group (n=4). Free T3:free T4 ratios were also analysed with dosages of levothyroxine. A control group was hormonally examined only once, but each of the patients with hypothyroidism was frequently examined.

Results: Serum thyroid hormones were determined as; i) control: fT3 3.51±0.51, fT4 1.29±0.20, TSH 2.31±0.98, fT3/fT4 2.78±0.56, ii) severe CH: fT3 3.78±0.60, fT4 1.64±0.32, TSH 2.52±2.02, fT3:fT4 2.35±0.46, iii) mild CH: fT3 3.48±0.42, fT4 1.69±0.26, TSH 2.45±1.69, fT3/fT4 2.11±0.38, iv) PHP: fT3 2.56±0.68, fT4 0.95±0.24, TSH 0.03±0.05, fT3/fT4 2.86±1.06. Free T4 levels of two CH groups were significantly higher than those of a control group. Free T3:free T4 ratios of two CH groups were significantly lower than that of a control group. Free T3:free T4 ratios of two CH groups were negatively correlated with dosages of levothyroxine.

Conclusion: This study suggested that levothyroxine monotherapy might maintain different conditions of peripheral thyroid hormones from physiological state in CH patients.

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