A New Radioimmunoassay Method for Serum Triiodothyronine using Sephadex G25 Column

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Abstract

A new method for the measurement of triiodothyronine (T3) in sera was described. All through the assay, a small column of Sephadex G25 suspended in 0.1N NaOH was employed. After the preparation of the column in 2.5ml syringe, 250μl 0.1N NaOH solution containing 125I-T3, 100μl standard solution and 100μl T3-free serum or sample serum were added and passed through the column. After washing out with 2.0ml of 0.063 M phosphate buffer pH7.4, 0.4ml diluted antiserum (1: 300) was added. The column was counted by a well counter (the first count). After 1hr incubation, the column was washed again with 1.5ml phosphate buffer. The second count of the column representing unbound T3 radioactivity was performed. Percent retention was calculated from the ratio of the second to the first count. Percent retention was shown to relate to the dose of T3 in the range from 31.3 to 1, 000pg/100μl.<BR>The concentration of T3 in sera of 12 normal, 4 TBG-deficient, 9 hypothyroid, and 13 hyperthyroid subjects was 148.3±24.4, 52.5±20.7, 53.3±27.2 and 425.4±110.8 ng/100ml (mean±SD), respectively.

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