Types of Urine Drug Testing

Abstract

Urine drug screening is typically a two-step procedure. The first step uses commercially available immunoassay to detect the presence of a drug or metabolite in the urine. Once specimens are identified as positive they have to be confirmed using gas chromatography/mass spectrometry [33]. The first stage analysis is known as a screening method performed by the “Enzyme Linked Immuno Sorbant Assay” (ELISA) that detects not only traces of drugs but also their metabolites. It is important to note, that the time-span where drugs can be detected as positive varies in regard to the specimen being used for screening (Fig. 10). The specificity and sensitivity of immunoassays vary depending on the type of assay and on the specific test being performed. The primary disadvantage of immunoassays is that the antibodies are seldom specific to one single drug or one drug metabolite. Therefore, the antibodies may bind with other substances. It is because of an immunoassay based positive result the term “presumptive positive” is being used since other factors such as cross-reactivity and difference in sensitivity and specificity among immunoassays does exist. Such results must be confirmed by a more specific method.