Does toxicology screening improve outcomes? What do the results mean?

A lot of time and money is spent collecting urine or saliva samples. Service users often see testing as a sign of mistrust and find the process somewhat humiliating. Some staff feel embarrassed and collect samples as part of a protocol whose purpose they do not fully understand: other staff are clear about the purpose and use each collection as an intervention opportunity. Obviously toxicology screening provides a record of drugs detected but there is much more to it:

  • Because collecting samples can be embarrassing or can be met with hostility, it is an opportunity to build relationships by having an informal, personal conversation.
  • The practitioner collecting a sample can make the contact a motivational moment by taking care to explain the purpose and making the service user feel comfortable.
  • Interpreting the results of screening can be difficult. Detection depends on the half life of the drugs, the frequency of drug use, the sensitivity of the screening test, and the frequency of testing.

Toxicology screening offers a qualitative and semi-quantitative indication of substance use.  There is good agreement (63-92%) between urine testing and self-report of drug use ⓵, however, this depends on both the substance and the circumstances in which testing occurs.  For example, asking an individual new to drug treatment services about their illicit drug use is likely to yield less reliable results to the same questions asked in the context of a long-term, supportive therapeutic relationship. Equally someone who is concerned about having their children taken away or their prescription stopped is unlikely to be forthcoming about any illicit drug use. The most common uses of toxicology are:

  • As the main outcome measure in treatment or research.
  • To detect relapse at an early stage
  • To detect supplementation of a substitute prescription
  • To assure abstinence in people with high risk occupations eg pilots, oil rig workers
  • To assure abstinence in people posing a risk to others eg child safety, violence

If someone is taking illicit drugs daily then detection is relatively easy and will probably have been noticed as intoxication or withdrawal without doing any toxicology screening.  Mathematical models of drug use patterns and drug screening schedules show that infrequent drug use is difficult to detect regardless of testing frequency, and that the benefits of more frequent drug testing are greatest with moderate levels of drug use. Suppose a drug can be detected for 24hrs and testing occurs every 2wks then the chance of detecting illicit drug use for someone using x2 weekly is approx. 5%, using weekly 25%, using twice weekly 50%, using every other day 70% ⓶. Where toxicology screening is used as a primary outcome measure the frequency of testing and the expected substance use detection rates need to be stated.

⓵ Darke S. (1998) Self-report among injecting drug users: a review. Drug and Alcohol Dependence 51: 253-263 PMID:9787998

⓶ Crosby RD, Gregory CA, and Specker SM. (2003) Simulation of drug use and urine screening patterns. Journal of Addictive Diseases 22: 89-98 DOI: 10.1300/J069v22n03_08