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Thyroid function in healthy Thai neonates
P Mahachoklertwattana1, A Sriphrapradang, S Supapannachart
1Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
Objectives:
To construct a normative data for serum thyroxine (T4), free T4 (FT4), triiodothyronine (T3) and thyrotropin (TSH) in Thai neonates.
Study Design:
A cross-sectional study of 275 healthy full-term neonates was conducted. Blood samples were obtained from umbilical cords of the neonates and from heel pads of infants aged 1-30 days. Hormone measurements included serum T4, FT4, T3 and TSH.
Results:
Mean serum T4 and FT4 levels rapidly increased after delivery to the maximum level at 1-3 days of age. Thereafter, they declined to a steady state level within 2-4 weeks. Mean serum T3 level was very low at birth. The concentration increased 3-5 times and reached a steady state levels within 1 week. In contrast, mean serum TSH declined from birth and the level at 1-3 days of age was slightly less than that of the cord blood. It changed little after 3 days of age. Previous studies have shown a transient TSH surge in the first 24-48 hour of life. TSH surge was not apparent in our study because samples were not obtained from infants < 24 hours old. Therefore, if TSH is measured for screening of congenital hypothyroidism, samples should be obtained from umbilical cord or infants aged > 48 hours.
Conclusions:
This study provides the normative data for thyroid function tests in Thai full-term neonates. These data are useful for detection and verification of hypothyroidism in a screening program for congenital hypothyroidism.