Screening for drugs of abuse. I: Opiates, amphetamines and cocaine.

(1) In order to provide an efficient and reliable service for drugs of abuse screening in urine, the laboratory should analyse 20-30 samples per week, and the staff should include a scientist with special expertise in the subject. (2) Turnaround times should be between 2-3 days of sample collection. To achieve this aim it may be necessary to make special arrangements for the delivery of samples to the laboratory. Results should preferably be transmitted by electronic mail or facsimile with the necessary precautions for security and confidentiality: hardcopy reports may also be required. (3) Good communications between the requesting clinician and the laboratory are essential. An advisory service should be provided by the laboratory and clinicians should be encouraged to discuss requests and results with laboratory staff. It is important that the laboratory inform doctors of the range of substances detected and the sensitivity and specificity of laboratory assays. (4) Assays should be performed according to the manufacturer's protocols, or by modified methods that have been rigorously validated. Quality control samples should be included in each analytical run and participation in an external quality assessment scheme, e.g. UKNEQAS, is essential to provide independent confirmation and confidence that results compare with those from other laboratories. Other requirements include adequate training and supervision of staff, and careful recording of samples and results. (5) Drugs to be tested will depend on the drug 'scene' in the area but should include those drugs regularly prescribed for maintenance therapy (e.g. methadone, dihydrocodeine, benzodiazepines), and drugs frequently misused (e.g. heroin, buprenorphine, amphetamines, cocaine). (6) Positive results obtained by preliminary screening methods e.g. EMIT, should be confirmed by another analytical technique, e.g. TLC, GC or GC-MS. If there are potentially serious or legal implications, and in employment and preemployment testing, confirmation of positive results is mandatory. In some cases, e.g. checking for methadone or benzodiazepine compliance, it may be considered unnecessary to confirm positive results although possible spiking of samples cannot be excluded without checking for the presence of metabolites by a chromatographic procedure.