Variation in values for iodothyronine hormones, thyrotropin, and thyroxine-binding globulin in normal umbilical-cord serum with season and duration of storage

Abstract

Concentrations of thyroxine, triiodothyronine, reverse triiodothyronine, thyroxine-binding globulin, and thyrotropin in pooled samples of cord sera from normal newborns were measured. Sera collected in winter contain significantly (p<0.05) higher concentrations of the first four - 14.9, 13.4, 9.5, and 7.5%, respectively - than do sera collected in summer; thyrotropin concentrations are similar in samples collected during winter and summer (p>0.05). With storage, the values for the thyronines and thyrotropin decreased progressively at rates between 0.9 and 5.3% per year; those for thyroxine-binding globulin did not change significantly.