Thyroid function in healthy Thai neonates.
OBJECTIVE
To construct a normative data for serum thyroxine (T4), free T4 (FT4), triiodothyronine (T3) and thyrotropin (TSH) in Thai neonates.


METHODS
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.
Mahachoklertwattana
P
P
Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
Sriphrapradang
A
A
Supapannachart
S
S
Pongsuwan
A
A
Choubtum
L
L
Rajatanavin
R
R
D003430:Cross-Sectional Studies; D006801:Humans; D007231:Infant, Newborn / Q000502:physiology*; D012016:Reference Values; D013785:Thailand; D013960:Thyroid Function Tests; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine