Free thyroxine index in maternal and cord sera: coefficients of variation evaluated by the method of differences of duplicates.

Abstract

Evaluation of thyroid function in the newborn may be critical for patient care. In the newborn, the normal ranges for protein-bound iodine, butanol-extractable iodine, thyroxine, triiodothyronine uptake and free thyroxine as reported in the literature have shown diagnostic discrepancies. The free thyroxine index, an estimate of the free thyroxine, was determined on paired sera from 30 healthy newborn infants and their mothers. The values of the free thyroxine indexes in infants and mothers were within the adult normal range for our laboratory.