Measurements of the Effective Thyroxine Ratio (ETR) in the Neonate, Infant, and Child

The applicability of the effective thyroxine ratio (ETR) was assessed in euthyroid neonates, infants, and children. ETR determinations on cord blood fell within the normal adult range. . In contrast, ETR values of newborns age 4 hr to 2 days were all elevated (1.17—1.37) and within the hyperthyroid range for adults. Values in infants age 2 weeks and older and in children age 1—15years all fell within the normal adult range. These findings suggest that the ETR can be used as an ancillary measure of thyroid func. tion in infants and children. In the immediate postpartum period, however, ETR values may be normally in the adult hyperthyroid range. Most methods for measuring circulating levels of thyroxine (T4) can be affected by alterations in con centrations of thyroid-binding proteins. Elevations of thyroid-binding globulin (TBG) levels, therefore,