EIA (Enzyme Immunoassay)

The EIA assay is a homogenous enzyme immunoassay technique used for the analysis of specific compounds in biological fluids 5. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6P-DH) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH, resulting in a absorbance change that is measured spectrophotometrically.