Enhanced specificity for small molecules in a convenient format which removes a limitation of competitive immunoassay.

Anti-complex immunoassay systems for small molecules permit the exquisite specificity achievable with monoclonal antibodies to be expressed to an extent which is not possible with competitive format immunoassay. While our previously reported anti-complex system is superior to competitive systems in terms of sensitivity, precision and specificity we have found that this specificity may be enhanced dramatically by simply interposing a wash step between the addition of sample and that of the labelled anti-complex antibody. When such a wash step was attempted with the competitive format system, after addition of sample but before addition of the labelled component, assay performance was degraded to the extent of making it unusable. We suggest, therefore, that the inherent flexibility of the anti-complex approach for small molecule assay creates an opportunity for remarkable enhancement of the functional specificity of primary antibody.