Serum thyroxine estimation: clinical evaluation of a modified semiautomated method and its ability for differential diagnosis of thyroid diseases.

A modified semiautomated microchemical method for determining serum thyroxine has been described. It consists of the isolation of T4 on a column of cation exchange resin Dowex 50 W X 2 and of a fully automated determination of iodine in the ammoniacal eluate from the column after an acidic mineralization. The diagnostic value of the method has been evaluated on a small group of patients examined for suspected thyroid gland dysfunction, in comparison with a parallel determination of T4 by a CPBA method (Tetrasorb test kit). From the results it follows that the microchemical method gives the results something inferior in comparison with the CPBA technique. The differences of means between the basic diagnostic groups of patients (euthyroids, hypothyroids, and hyperthyroids) in both methods were statistically significant. The extent to which these tests can discriminate was investigated at a 5% discrimination threshold. The discriminatory ability of both methods between hyperthyroidism and euthyroidism is nearly the same. The CPBA method discriminates euthyroids from the hypothyroids better, the results of both tests, however, do not differ too much. It seems to be confirmed that irrespective of the method used, the determination of serum T4 itself can detect neither hyperthyroidism nor hypothyroidism reliably. The possible causes are discussed in this paper.