Cross reactivity analysis immunoassay development, specificity

Beta-endorphin is a frequently measured opioid peptide. Immunoassay is the method of choice for the analysis of plasma (3-endorphin. Both RIAs and direct IRMAs have been developed for this purpose. Commercial reagent kits are widely available, and many commercial reference laboratories offer P-endorphin assays. The concentrations of P-endorphin are usually very low to undetectable in normal subjects, and it may be necessary to use extraction procedures to detect meaningful concentrations in plasma. The specificity of commercial antibodies for p-endorphin relative to p-LPH varies widely in some immunoassays, 50% cross-reactivity is seen with p-LPH. With polyclonal antibodies, results may be spuriously high owing to crossreactivity with serum immunoglobulin G (e.g., in patients with immunoglobulin G myeloma). 

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