Work simplification of a competitive protein binding analysis for serum thyroxine, and a study of some laboratory factors affecting assay results

Abstract

The work simplification of competitive protein binding (CPB) analysis for serum thyroxine is described. Modification and design of apparatus specifically for use in the assay adds gieatly to the convenience and reliability with which large workloads can be handled. Forty patient samples plus controls can be easily analysed by one person in 4 h. The simplified CPB working method is accurate, but, in comparison with an automated protein bound iodine (PBI) method, is somewhat inferior in precision and shows a slightly greater cost per analysis. Serum samples for CPB analysis were stable if stored at + 4° or — 20° for periods of up to 14 days. Storage at room temperature for two days or longer, however, resulted in an increase of about 19 nmoles/1 in the assay result. Haemolysis at the levels occasionally encountered in laboratory specimens was without any detectable effect on the assay result.