Serum thyroxine by competitive protein binding analysis: clinical, statistical and comparative evaluation.

Abstract

ABSTRACT Serum thyroxine by competitive protein binding analysis (T4 by CPBA) furnishes a highly sensitive and specific method for measuring serum thyroxine. In addition, the assay is relatively simple, rapid, and does not require the presence of patients since it is an in vitro test. Spurious results due to iodine containing contrast material and other iodine compounds not infrequently seen with certain other tests of thyroid function are avoided. Mean thyroxine iodine (T4I) by CPBA in a series of 129 euthyroid “normals” was 6.1±1.4 (sd), T4 by column 5.6±1.6 and PBI 6.1±1.1. Standard deviations for replicate samples were 0.27, 0.79 and 0.39, respectively, for the 3 methods. Fourteen hyperthyroid patients had an elevated T4I by CPBA and PBI. Seven per cent of euthyroid individuals had a spuriously elevated PBI, but all of these had normal T4I by CPBA. Eight of 9 hypothyroid patients had a low T4I by CPBA, but one clearly myxedematous patient had a borderline normal value. Two of the hypothyroid patients ...