Immunoassay screen for qualitative detection of the opiate in urine.

Opiate compounds, such as morphine and codeine, are naturally occurring alkaloids of opium and are widely used as analgesics. Although drug abusers may abuse morphine and codeine, another opiate compound, heroin, is synthesized from morphine and is the most commonly abused opiate. When ingested or injected, heroin is metabolized to the molecule, 6-Monoacetyl morphine (6-AM or 6-MAM), which is hydrolyzed back to morphine. Opiates are rapidly metabolized by the body and excreted in urine, allowing immunoassays to detect recent use of morphine, codeine, and/or heroin. 

The opiate screening assay uses monoclonal antibodies that detect opiates in urine. The assay is based on the competition between an enzyme glucose-6-phosphate dehydrogenase (G6PDH) labeled drug and the free drug from the urine sample for a fixed amount of specific antibody binding sites. In the absence of free drug from the sample, the specific antibody binds the drug-labeled G6PDH and the enzyme activity is inhibited. This phenomenon creates a direct relationship between drug concentration in urine and enzyme activity. The enzyme G6PDH activity is determined spectrophotometrically at 340 nm by measuring its ability to convert nicotinamide adenine dinucleotide (NAD) to NADH.