ESPE Abstracts

Background: As newborn screening test (NST) became popular, the incidence of congenital hypothyroidism (CH) was raised. But not all CH children require lifelong levothyroxine (LT₄) replacement therapy.

Objective and hypotheses: We aimed to analyse predicting factors suggesting transient CH (TCH) compared to permanent CH (PCH) or transient thyroid function test (TFT) abnormality who had a positive screening results in our centers for the past decade.

Method: 105 subjects (50 boys) who had an elevated TSH levels detected by NST were enrolled. Biochemical and imaging results, and treatment histories were reviewed retrospectively. TCH was defined when trial-off therapy was successful and kept their TFT within tolerable range at least 6 months of follow-up. PCH was defined when trial-off therapy was failed or kept on medication over 3 years of age. Transient TFT abnormality was defined when the subjects did not require LT₄ replacement therapy and their follow-up TFTs were normalised.

Results: CH was diagnosed in 75.2% (TCH 35.2% and PCH 40.0%) and the rest (24.8%) of the newborns showed transient TFT abnormality. Thyroid sonography or scintigraphy was performed in 78 subjects with CH and results were abnormal in 56.4% (n=44/78). Initial NST-TSH level (cutoff, 31.0 μIU/ml), LT₄ dose at 2 years of age (4.1 μg/kg per day), and maximal LT₄ dose (50 μg/day) revealed as significant predictive factors discriminating between TCH and PCH. While, initial serum level of fT₄ (1.06 ng/dl), not TSH levels, was the only factor to discriminate between transient TFT abnormality and TCH.

Conclusion: As both NST-TSH level and treatment histories are important to predict a successful trial-off therapy in CH patients, the earlier re-evaluation might be possible when their initial NST-TSH level, maximal or 2-year-age LT₄ doses are low. And when initial serum level of fT₄ is above the average values in a neonate with mild elevation of TSH level, follow-up without LT₄ medication could be considered. Lastly, NST-TSH cutoff values might be readjusted to prevent unnecessary or over-treatment of TCH with normal thyroid gland.