Thyroid Function Assay Using the Effective Thyroxine Ratio (ETR) in Infancy

Abstract

Effective thyroxine ratio (ETR) and total serum thyroxine (T₄) estimations have been performed on 119 healthy infants divided into three groups according to birthweight and gestational age (normal, small-for-age, and preterm). ETR and T₄ were determined at 1 and 5 days and at 1, 3, 6 and 12 months. During the first month the values of both ETR and T₄ were significantly higher than at the age of 3 months and later. This marked postnatal spurt of thyroid activity, which is probably due to increased secretion of the thyroid-stimulating hormone, was slightly lower in small-for-age and preterm infants than in fullterm ones. From the age of 3 months onwards the values of both ETR and T₄ were similar to those of adults.

Key Words:

• Effective thyroxine ratio
• infancy
• serum thyroxine
• thyroid function tests