Serum thyroid stimulating hormone, total and free T4 during the neonatal period: Establishing regional reference...

Congenital hypothyroidism (CH), the most common etiology of preventable mental retardation in children, is estimated to be more prevalent among Asian population.

Since thyroid function tests (TFTs) varied among different ages and geographical regions, in this study, the neonatal thyroid reference intervals in a healthy neonatal population is determined for the first time in Iran.

A cross-sectional study performed on 246 healthy term newborns aged between 2 days and 1 month.

Blood samples were obtained by venipuncture from all subjects. The median, 2.5(th), 5(th), 95(th), and 97.5(th) percentile of serum thyroid-stimulating hormone (TSH), as well as the total and free T4 were assessed among different age groups.

Predictive Analytics Software (PASW Statistics 18) was used for the analysis.

Serum TSH, total and free T4 concentration peaked in 5(th) to 7(th) days of life, continued over 2 weeks, then decreased and started reaching to adult reference range. A significant negative correlation between age and serum concentration of TSH (P = 0.02), total T4 (P = 0.01) and free T4 (P = 0.01) was found.

This study yielded fairly different values for TFTs compared compared values found in other countries and also different from values reported for laboratory kits we used. These differences were assumed to be due to variations in ethnicity, age, and laboratory methods used. Due to the lack of international standardization, conducting multicenter studies helps in making a more precise evaluation of thyroid status in neonates.