Interactions among enzyme, antibody, drug, and time in enzyme immunoassays for drugs of abuse.

Published information on the major interactive variables of enzymic immunoassays for drugs, whether in urine or serum, is scanty. Using the Syva EMIT-dau Barbiturates assay as an example, we examined the following interactive variables with respect to test response: concentrations of enzyme, antibody, and drug; urine matrix; and time. The results suggest a process for optimizing this type of enzyme immunoassay. Transformation of the data gives indirect evidence of heterogeneous antibody reactions that are drug-concentration dependent.