RADIOIMMUNOASSAY OF FREE-THYROXINE WITH PREBOUND ANTI-T4 MICROCAPSULES

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 20  (9) , 956-960
Abstract
Free thyroxine (FT4) may be 1 of the active thyroid hormones in contact with target end organs. It is unaffected by alterations in serum protein levels. In most cases, measurement of FT4 reflects an individual''s true thyroid function or dysfunction. Previous FT4 assay techniques were difficult, tedious, indirect and inaccurate. A rapid, simple, and accurate radioimmunoassay for FT4 was developed using microencapsulated rabbit anti-T4 antiserum to which 125I-T4 tracer of high specific activity was complexed. Addition of FT4 standards or unknown samples displaces a proportional amount of 125I-T4 from antibody. Protein-bound T4 is excluded from the reaction by short incubation time and spatial configurations. Subjects [human] representing known thyroid dysfunction were tested using the above procedure. The normal range of FT4 was 0.8-2.4 ng/dl. The mean FT4 for the hyperthyroid group was 6.92 .+-. 1.38 (range 4.4-9.6) ng/dl. The mean FT4 for the hypothyroid group was 0.43 .+-. 0.37 (range 0.1-1.3) ng/dl, and in pregnancy the mean FT4 was 1.64 .+-. 0.44 (range 1.0-2.2) ng/dl.