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Analytical requirements , Immunoassays

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  253

2026-10-19

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Analytical requirements

Immunoassays

Immunoassays, as conventional separation radioimmunoassays, have been applied to the determination of therapeutic drugs since the late 1960s, and these techniques still have a role when very high sensitivity is required. However, the advent of homogeneous (not requiring a phase separation step) non-isotopic immunoassays in the mid-1970s proved to be the foundation for widespread adoption of commercial immunoassay kits into clinical laboratories. A bewildering variety of techniques are now available. These kits have obvious advantages. They are generally technically simple, require little operator skill and are amenable to automation on equipment commonly found in routine clinical laboratories. Sample throughputs can thus be very high, and analysis times very short. Their main disadvantage is lack of specificity, either because of interference from endogenous plasma components (haemoglobin, bilirubin, etc.), which can affect the efficiency of the detection system, or because of cross-reactivity of the primary antibody with metabolites or structurally related compounds. Drugs with a large number of metabolites with similar structures (e.g. benzodiazepines, ciclosporin) pose particular problems in this respect. The development of sophisticated homogeneous non-isotopic systems is now virtually exclusive to large commercial organisations, which limits the practical applicability of immunoassays to compounds for which there is a commercial market for an assay system. It is important to realise that the cross reactivity, selectivity and sensitivity of the available immunoassays may vary, even with the same technique. It was found that FPIA on Abbott’s AxSym too often produced false positive results (controlled by GC-MS) whereas FPIA on Abbott’s TDx (same samples) did not provide false positive results.