Ashkar F S, Buehler R J, Chan T, Hourani M
J Nucl Med. 1979 Sep;20(9):956-60.
Free thyroxine (FT4) may be one of the active throid 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 have been difficult, tedious, indirect, and inaccurate. A rapid, simple, and accurate radioimmunoassay for FT4 has been developed using microencapsulated rabbit anti-T4 antiserum to which I-125 T4 tracer of high specific activity has been complexed. Addition of FT4 standards or unknown samples displaces a proportional amount of I-125 T4 from antibody. Protein-bound T4 is excluded from the reaction by short incubation time and spatial configurations. Specimens 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 of 1.0-2.2) ng/dl (1).
游离甲状腺素（FT4）可能是与靶终末器官接触的活性甲状腺激素之一。它不受血清蛋白水平变化的影响。在大多数情况下，FT4的测定反映了个体真实的甲状腺功能或功能障碍。以往的FT4检测技术操作困难、繁琐、间接且不准确。现已开发出一种快速、简单且准确的FT4放射免疫分析法，该方法使用微囊化兔抗T4抗血清，其已与高比活度的I-125 T4示踪剂复合。加入FT4标准品或未知样品会从抗体上置换出成比例的I-125 T4。通过短孵育时间和空间构型将结合蛋白的T4排除在反应之外。使用上述方法对代表已知甲状腺功能障碍的标本进行检测。FT4的正常范围为0.8 - 2.4 ng/dl。甲状腺功能亢进组的平均FT4为6.92 +/- 1.38（范围4.4 - 9.6）ng/dl。甲状腺功能减退组的平均FT4为0.43 +/- 0.37（范围0.1 - 1.3）ng/dl，孕期的平均FT4为1.64 +/- 0.44（范围1.0 - 2.2）ng/dl（1）。
