Techniques for improving the specificity of sandwich enzyme-linked immunosorbent assay-based drug screening.

ELISA assays are commonly used for drug screening by racing laboratories but are known to suffer from limited specificity. Inaccurate ELISA screening results are typically produced by non-specific antibody interactions or by the retention of chromogenic material in the sample well due to sample degradation. While confirmation of drug positives can be achieved by mass spectrometry, the follow-up of inaccurate ELISA screening results represents an unnecessary cost in staff time and reagents. This is particularly true in the case of rhEPO screening using sandwich ELISA assays, where the confirmation method requires up to 3 days to perform. While most racing laboratories purchase commercial ELISA kits, these products can be customised to provide increased specificity for enhanced screening of positive samples. The specificity of commercial sandwich ELISA kits can be improved by a variety of mechanisms including the addition of competing analyte specific antibodies, substitution of capture antibodies or by performing ELISA analysis with and without capture antibodies. Non-specific signals in difficult matrices such as canine urine can also be reduced by the addition of BSA solutions to the ELISA plate prior to the addition of samples.