Comparison of Biological and Chemical Assay of Thyroid

The biological and chemical examination of thyroid samples has demonstrated the inadequacy of the B.P. assay, which is based upon the determination of so-called “thyroxine iodine”. It is suggested that, in the absence of specific methods for determining thyroxine and tri-iodothyronine in thyroid, the chemical assay should be replaced by a biological assay.The mouse anoxia method is shown to be suitable for this purpose. The potencies of samples assayed thus over the past 3 years, together with chemical data and clinical comments are presented. The relative activities of the thyroid constituents 3,5,3′,5′-tetra-iodo-L-thyronine (L-thyroxine), 3,5,3′-tri-iodo-L-thyronine, 3,5-di-iodo-L-tyrosine, 3-mono-iodo-L-tyrosine, as determined by the mouse anoxia method, are in good agreement with their reported clinical effectiveness.