Recent advances in radioimmunoassay and related procedures

For hapten assays, general solutions to the problem of bridge recognition now offer the prospect of replacing tritiated tracers by externally labelled ones, initially using 125I. Direct assays for blood steroids are emerging successfully to remove the need for laborious and error-prone extraction. The provision of monoclonal antibodies (MAb) now renders practicable the inherently superior immunometric methods, among which two-site 'sandwich' assays are preferred. The specificities of these assays depend centrally upon the use of MAb which react with a single epitope on the antigen. On the limited evidence thus far accumulated, reservations about the specificity of systems based upon substituting such an end-point for that given by the multiplicity of binding sites involved when using conventional heterogeneous antibodies are beginning to seem groundless. Antibody-coated tubes and beads which provide limited binding capacity and hence very limited working ranges are useful for yes/no assays: finely particulate support media are better for graded-dose assays. The advantages of these MAb-based immunoradiometric assays (IRMA) are rapid response times, shorter counting times, wider working ranges and lower detection limits, better specificity, minimal non-specific serum effects, high practicability and assured reagent continuity. Although no generally successful approach to the full automation of immunoassay procedures has yet emerged, there has been a steady advance in work-simplification equipment. Automated data reduction is now commonplace. Some systems, particularly those to which a microprocessor is coupled and sold with the detector, are dangerously simplistic and do not allow the user access to the underlying computing mechanisms. Much work is being done on alternatives to radiolabelled tracers