Method Description

Opiates exist in patient urine as both free and either sulfate or glucuronide conjugates. Specimens are initially screened by immunoassay. The opiate assay is based on the kinetic interaction of microparticles in a solution as measured by changes in light transmission. In the absence of sample drug, soluble drug conjugates bind to antibody-bound microparticles, causing the formation of particle aggregates. As the aggregation reaction proceeds in the absence of sample drug, the absorbance increases. When a urine sample contains the drug in question, this drug competes with the drug derivative conjugate for microparticle-bound antibody. Antibody bound to sample drug is no longer available to promote particle aggregation, and subsequent particle lattice formation is inhibited. The presence of sample drug diminishes the increasing absorbance in proportion to the concentration of drug in the sample. Sample drug content is determined relative to the value obtained for a known cutoff concentration of drug.

The NADH formed during the reaction, measured photometrically as a rate of change in absorbance, is directly proportional to the ethyl alcohol concentration.(Package insert: OPI2. Roche Diagnostics; V 16.0 01/2022)

After screening, enzyme hydrolysis is used to liberate the conjugated drug. Specimens are then centrifuged, diluted, and the analytes are separated by liquid chromatography tandem mass spectroscopy and analyzed by multiple reaction monitoring.(Unpublished Mayo method)