Urine testing for drugs of abuse has been routinely used in substance abuse testing programs for many years. Targeted compounds in urine are often drug metabolites, generated as a result of drugs being actively converted in the body into new compounds in order to promote their elimination.
In general, many drugs and their metabolites can be detected in urine for up to 3 or 4 days after use. There are some notable exceptions however - cannabis metabolite, for example, can potentially be detected for up to several weeks following heavy cannabis use. Alcohol and the main heroin metabolite (acetylmorphine) are usually eliminated within 12 hours.
A sample of urine is collected using a sampling kit designed for this purpose. Although direct observation of the collection is not usually appropriate, measures are taken to minimise the potential for sample adulteration or substitution. The collection facility is suitably prepared prior to collection taking place - donors are asked to wash their hands before collection, access to water taps is controlled and the temperature of the collected sample is monitored.
In addition to these measures, each sample is routinely analysed in the laboratory for adulteration/dilution markers before analysis begins.
Collection is carried out under full chain-of-custody conditions. Before the collected sample is labelled and sealed, it is divided into several portions, one of which is retained unopened in the laboratory in case of dispute.
A sample of the submitted urine is initially screened in the laboratory for a number of target drug groups. If screening analysis presumptively detects drugs at a concentration that exceeds pre-defined cutoffs, another portion of the sample is taken and processed for confirmatory analysis.
This confirmatory analysis is specifically directed towards individual members of the drug groups that were found to be non-negative at the screening stage. Confirmatory analysis is carried out using highly specific techniques capable of identifying individual drugs with absolute certainty and measuring their concentrations.
If the concentrations of confirmed drugs are above pre-defined cutoffs, a positive laboratory report is issued. If the drugs detected are consistent with medication declared at the time of collection, this is reflected in the laboratory report. If drugs resulting from prescribed medication are detected, the donor should be able to demonstrate legitimate prescription.
If either the screening or confirmatory results are such that drug concentrations lie below the defined cutoff values, no further work is undertaken and a negative laboratory report is issued.
Cutoff concentrations are used to distinguish those samples that are to be considered negative or positive. Such interpretative cutoffs are commonly used in the drug testing industry for workplace and substance abuse casework and cutoffs for many common drugs have been defined in industry guidelines (eg. European Workplace Drug Testing Society (ewdts.org)).
These cutoffs are usually applied in the laboratory and their application enables drug test results to be used to identify drug use with a high probability; passive or low level exposure is likely to result in a negative outcome.
Quantitative results are reported in such a way that allowance has been made for analytical variation.
Cutoffs may also be represented by the sensitivity of the analytical method and in these cases expert interpretation of the results is provided. This can occur for example where cutoffs for a particular drug have yet to be defined within the drug testing industry.
Urine - Scope of Analysis
The drugs included in the analytical panels include the majority of common drugs of abuse and alcohol. Special targeted analysis for unusual drugs is also available on request and may be appropriate in the testing for specific drugs or New Psychoactive Substances (NPS).
Urine - Alcohol Markers
Urine testing for alcohol markers (EtG and EtS) can be useful in some circumstances, particularly when recent abstinence has been claimed. These compounds are minor metabolites of alcohol and can be detected in urine after alcohol has been eliminated. EtG can be detected in urine for up to about 48 hours, even after consumption of small quantities of alcohol; after excessive consumption the window of detection can be longer. EtG and EtS levels in urine cannot distinguish between a binge drinking event several days beforehand and minor alcohol intake a few hours before the sample was taken.