Faix J D, Rosen H N, Velazquez F R
Department of Pathology, Harvard Medical School, Boston, MA.
Clin Chem. 1995 Jan;41(1):41-7.
There are many alternative ways of estimating free thyroxine (T4) when thyrotropin screening results are abnormal. In addition to free T4 immunoassays, the menu of most automated immunoassay instruments includes a nonisotopic version of the original triiodothyronine (T3)-uptake assay called "T-uptake." We evaluated the ability of five such assays (Access, ES-300, IMx, Magnum Opus, and Stratus) to accurately estimate the free thyroxine index (FTI) in euthyroid, hyperthyroid, and hypothyroid patients with abnormal concentrations of thyroid hormone-binding proteins, and in patients with nonthyroidal illness. For comparison, we calculated a similar FTI, using either T3-uptake or direct measurement of thyroxine-binding globulin (TBG). Euthyroid reference ranges were comparable. Of euthyroid patients with increased TBG, 12-32% and 5-20% had increased or suppressed FTI, respectively, depending on the T-uptake method used. Except for IMx, 6-35% of hypothyroid patients with increased TBG had inappropriately increased FTI. Patients with nonthyroidal illness had comparable results regardless of the method used, and T-uptake methods were variably affected by known inhibitors of thyroid hormone binding. The most reliable T-uptake method appeared to be the IMx, which, despite claims that it measures all thyroid hormone-binding proteins, correlated best with TBG concentrations.
当促甲状腺激素筛查结果异常时，有许多替代方法可用于估算游离甲状腺素（T4）。除了游离T4免疫测定法外，大多数自动免疫测定仪器的菜单中还包括一种原始三碘甲状腺原氨酸（T3）摄取试验的非同位素版本，称为“T摄取”。我们评估了五种此类试验（Access、ES - 300、IMx、Magnum Opus和Stratus）在甲状腺激素结合蛋白浓度异常的甲状腺功能正常、甲状腺功能亢进和甲状腺功能减退患者以及非甲状腺疾病患者中准确估算游离甲状腺素指数（FTI）的能力。为了进行比较，我们使用T3摄取或直接测量甲状腺素结合球蛋白（TBG）来计算类似的FTI。甲状腺功能正常的参考范围具有可比性。在甲状腺功能正常且TBG升高的患者中，根据所使用的T摄取方法，分别有12% - 32%和5% - 20%的患者FTI升高或降低。除IMx外，6% - 35%甲状腺功能减退且TBG升高的患者FTI升高异常。非甲状腺疾病患者无论使用何种方法结果都具有可比性，并且T摄取方法受到已知甲状腺激素结合抑制剂的不同程度影响。最可靠的T摄取方法似乎是IMx，尽管有人声称它能测量所有甲状腺激素结合蛋白，但它与TBG浓度的相关性最好。
