Thyroid Function in Healthy Thai Neonates
PAT MAHACHOKLERTWATTANA, M.D.* SARAYUT SUPAPANNACHART, M.D.*, LULIN CHOUBTUM, B.Sc. **, ARPORN SRIPHRAPRADANG, B.Sc.**, AROONWAN PONGSUWAN, B.Sc.***, RAJATA RAJATANAVIN, M.D.****
Affiliation : * Department of Pediatrics, ** Research Center, *** Department of Nursing, **** Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok I 0400, Thailand.
Objectives : To construct a normative data for serum thyroxine (T4), free T4 (Ff 4),
triiodothyronine (T 3) 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 T 4, Ff 4, T 3 and TSH.
Results : Mean serum T4 and Fr4 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 T 3 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.
Keywords : Thyroid Function, Neonate, Healthy
