Principle
Urine samples are screened in the laboratory for a range of drug groups using immunoassay. These tests are 'group specific' and are designed to identify negative samples. If an immunoassay test for a particular drug group gives a positive result (ie a result above a defined threshold or cut-off value) then that sample is considered to be 'not-negative' and the positive result may be due to the presence of a drug. Those samples which screen positive are subjected to a second confirmatory test which is both specific and precise. If this test shows that a particular drug is indeed present and the concentration of the drug exceeds a defined threshold, then the sample is considered positive.
Analysis
Laboratory screening is carried out using a well established and accredited immunoassay system which is used to identify those samples which do not contain drugs. Confirmatory testing is highly specific and the individual drugs which may be present are identified and quantified using GCMS (gas chromatography mass spectrometry). Identification using this technique provides definitive evidence for the presence of the drug and can be used in court proceedings if necessary.
