Immunochemical Techniques in Clinical Analysis

Abstract

<p>In an attempt to develop a new sensitive immunoassay procedure to measure biologically important small molecular weight compounds in human plasma or serum, the principle of inhibition of antigen-antibody precipitation by free antigen as detected by automated nephelometry was investigated. The assay procedure was optimized for maximum sensitivity. The characteristics of the optimized system are described and with the available instrumentation, the lower level of detection of free digoxin (a cardiac glycoside) was shown to be 2 nanograms. The results demonstrate the successful application of the principle, but fall short of providing a reasonable alternate to the radioimmunoassay of digoxin in human plasma or serum for routine clinical use.</p> <p>A fast and cheap method for the separation of free and antibody-bound ligand, as applied to established radioimmunoassay techniques, was developed using chemically treated and heat-killed Staphylococcus aureus bacteria. In application to the measurement of a small molecular weight compound (digoxin) and a serum protein (ferritin), it was demonstrated to have good correlation with currently utilized techniques. This alternate method is shown to be suitable for routine clinical diagnostic purposes.</p>