DRUG-ABUSE SCREENING WITH IMMUNOASSAYS - UNEXPECTED CROSS-REACTIVITIES AND OTHER PITFALLS

Immunoassays are the only practical means of coping with the increasin g demand for drug abuse screening because of their simplicity and ease of automation. However, it is essential that the analyst understands the strengths and weaknesses of such assays to enable correct interpre tation of results. This is especially important with the increasing po pularity of near-patient testing where assays are liable to be carried out by inexperienced and untrained staff. False-positive and false-ne gative results, unexpected cross-reactivities and other pitfalls are d iscussed, together with an attempt to explain the reasons for these pr oblems.