110. critical reagent Essential component of an assay (particularly ligand-binding assays [LBAs]) whose characteristics are crucial to assay performance. These reagents may be specific capture reagents, antibodies, peptides and conjugates, and they require thorough characterization and documentation. Critical reagents may require significant amounts of time to acquire and/or to determine if suitable for use. They are usually analyte specific, difficult to replace and have a direct impact on the results of an assay.
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111. cross-reactivity In immunology, cross-reactivity refers to the reaction between an antibody and an antigen that differs from the antigen (analyte) of interest. It arises when a molecule has an epitope sufficiently similar to one on the analyte of interest to cause that molecule to bind to the antibody in a ligand-binding assay (LBA) in a similar way (with similar or different affinity) to the analyte of interest. Specificity is related to the concept of cross-reactivity. If an antibody is highly specific it has low cross-reactivity with molecules other than the analyte of interest.
