The Laboratory uses a range of carefully controlled chromatographic and immunoassay techniques for detecting and confirming the presence of drugs of abuse in urine specimens. The Laboratory aims to ensure a minimum of false 'negative' results, and that no false 'positive' results are reported. Confirmatory tests are always performed for the identification of specific amphetamine and opiate class drugs. However, in the cases of benzodiazepines, cannabis, cocaine and methadone, confirmatory tests are NOT routinely carried out, because these immunoassay are relatively specific and rarely produce false positives. Confirmatory test are, however, available for unexpected findings. The Laboratory is able to provide "absolute" confirmation of findings using gas chromatography-mass spectrometry techniques. The Laboratory participates regularly in external quality assurance schemes as part of an effort to achieve a consistently high standard of performance.

There is currently a profusion of near-patient testing devices that have been specifically targeted at drug dependency units and clinics. Some of these devices have been shown to produce accurate results. However, some devices suffer from inappropriate labeling, which together with the subjective interpretation of poorly defined reaction end-point markers, leads to misinterpretation of the results generated.

A literature search was conducted regarding the use and evaluation of near-patient testing devices for drugs-of-abuse screening. The results of this research, together our own practical evaluations of such devices, have been collated into this review.

It is proposed that although near-patient testing devices may be useful in remote areas or where rapid action needs to be taken, it should be remembered that they provide only initial screening data and may yield false-positive or flase-negative results. Such devices need to be used with caution because a rapid but unconfirmed result may lead to misdiagnosis and inappropriate treatment for those who have a drug problem. It should be noted that a single result, which may be inaccurate, could lead to the cessation of treatment and a failure to provide care for those in greatest need. In addition, false-positive results may also have medico-legal implications, especially with the initiation of the drug testing and treatment orders.

Near-patient testing devices for drugs of abuse could be an expensive and potentially inaccurate means to monitor patient treatment and drug abuse status.

The appropriate specimen for screening for drugs of abuse is a 'spot' urine sample (20-30 ml) which should be stored in a sterile plastic container without preservative. The patient's full name, hospital or other identification number, and the date and time of collection should be written clearly on the specimen container and on the request form. It is also important to record each client's full home postcode. Special care should be taken to ensure that the specimen obtained is authentic i.e. it has been freshly voided by the patient under supervision, and not subsequently adulterated or substituted for a "drug free" specimen. A urine specimen for drugs of abuse screening should be sent by courier or first class mail, but if there is likely to be a delay in dispatch, it should be kept in a 4oC refrigerator prior to being sent to the laboratory.

Screening for drugs of abuse (as distinct from the investigation of volatile substance abuse) is carried out with urine specimens. A wide variety of drugs will be detected qualitatively by the "standard" screening procedure. However, some other substances of abuse are not sought routinely, and in these cases, the laboratory test which is relevant should be requested specifically.

It should be noted that analysis of urine specimens for "drugs of abuse" will only give information about current or recent drug usage. A specimen taken more than a few days after an episode of 'abuse' is likely to be negative on screening for most substances, with the notable exception of cannabis.

The range of substances detected in the "standard" screening procedure includes controlled drugs (CD), prescription-only medicines, medicines available over-the-counter (OTC), and illicit drugs. Confirmation of the presence of specific substances will be routinely carried out where amphetamine and opiate class drugs are detected on screening.