Change of TSH, T4, and Free T4 Concentrations During the 48 Hours of Postnatal Period

Kim, Sung Soo; Lee, Jong Hyun; Lee, Dong Hwan; Choi, Tae Youn

Abstract

PURPOSE
Congenital hypothyroidism is the most common endocrine disease in infant period and if it is not treated in good time it would cause irreversible failure to thrive and mental retardation. For this reason neonatal screening test for diagnosis is critical in early infant. TSH concentrations which were performed to know thyroid functions normally or not increased rapidly at 30 minutes of life and then fell at 48 hours of life so it was considered inappropriate for neonatal screening test because of false positive result. Otherwise free T4 is not variable within 48 hours, and that's why authors proposed free T4 as an applicable way to early discharge neonates for neonatal screening test.
METHODS
We have performed this study to obtain normal TSH, T4, and free T4 concentrations in Korean neonates. Total 17 neonates were studied in Soonchunhyang University Hospital from March 2004 to June 2004. 17 samples were performed at 15, 30 minutes, 1, 2, 3, 4, 24, 48 hours of life from 17 neonates who have had no perinatal problem, medication history and mother's illness studied and the results were compared by applying enzyme linked immunosorbent assay.
RESULTS
In the early postnatal period, serum TSH concentrations increased rapidly to peak level (mean of 32.06 microIU/mL) at 30 minutes of life and then fell very gradually to mean concentration (mean of 4.18 microIU/mL) at 48 hours of life and serum T4 concentrations shows variable pattern but the mean values of T4 showed normal range of T4 (6.0-19.9 microgram/dL). On the other hand, serum free T4 concentrations increased to peak level (mean of 3.00 microgram/dL) at 24 hours of life and gradually decreased and it was observed that the mean values of free T4 maintained higher than the diagnostic criteria of congenital hypothyroidism (0.85 microgram/dL).
CONCLUSION
According to this result, we consider that free T4 is much more applicable way to early discharge neonates for neonatal screening test because of its slim variability.