Serum Effects on Thyroxine and Triiodothyronine Levels

Abstract

The aim of the investigation was to study the influence of serum of different species on commercial radioimmunoassays for T 4 and T 3. Therefore a largely T 4-and T 3-free serum or plasma of man, rat, pig, sheep, cattle, horse, dog, and chicken was produced. The standard method of extracting T 4 and T 3 from serum or plasma with charcoal led only to extraction results of 93 %. This could be improved to 99.5 % or more by using a batch-technique with a resin. The success of the extraction was controlled by labelled hormones in both cases.The largely T4-and T3-free sera or plasma were used in radioimmunoassays of various manufacturers. The results were influenced by the different species, indicating that the serum composition and the different binding fractions for thyroid hormones play a large part in the values obtained. This could be confirmed by a serum dilution with Tyrode's solution in the ratio of 1 : 1, which yielded false negative values in all cases investigated.The investigation showed that radioimmunoassays developed for human medicine cannot be used without adaptation to the special sera or plasma. Also a RIA designed for the dog could not be used for all species in veterinary medicine. The hormone values measured with unadapted testkits should therefore be doubted.