Preliminary tests for drugs of abuse.

A drug-testing program must be designed by the client in consultation with the laboratory. The test procedures selected for the analytes in question depend on the defined "cutoff" concentrations, equipment available, and turnaround time. Preliminary tests are needed to separate the large number of negatives from presumptive positives, which then have to be confirmed. Immunoassays done with random-access analyzers are the procedures of choice. In clinical situations, thin-layer chromatographic procedures may be favored. The attributes and liabilities of the various procedures are presented as guides to the selection of a suitable procedure for a particular client.