Drug and alcohol testing
Helping people to change requires us to start from the service user’s perspective and many will see drug testing as intrusive, punitive or stigmatising. So, drug testing needs to be communicated as a shared interest with positives for the service user. Practitioners need to have the knowledge to interpret test results correctly. Most drugs are eliminated in urine and so this is usually a reliable means of detection. Drugs can also be found in blood, breath, faeces, sweat, saliva, - any body fluid.
The aims of drug testing are to establish what drugs are being used and:
To ensure the safety of prescribing. Whether for substitute prescribing or detoxification, drug testing is there to reduce the risk of complications, for example from prescribing opiates or depressant type medication without knowing that benzodiazepines are already being taken. It is in the interest of the individual to be neither over- nor under-medicated.
To ensure that the service user has a useful tool to monitor their progress and has evidence of that achievement for their practitioner, friends and family.
To enhance motivation by providing objective evidence of progress towards goals which helps to build a working alliance.
How often should drug tests be done?
Obviously the more frequent and random the testing, the better the detection of all the drugs being taken. Frequent testing may not be feasible or desirable for everybody and decisions are best made case by case. The chart shows the expected detection rate for different frequencies of testing and different frequencies of substance use.
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. For example, if someone is using a drug with a 24hr detection window, say heroin or cocaine (see below re metabolites), 3-4 days a week, then weekly drug testing would be positive 95% of the time and monthly testing 50% of the time; if using the drug only once a week then weekly tests would be positive 50% of the time and monthly testing 14% of the time. Drugs with longer detection windows are more likely to be detected.
How drugs are metabolised…
When the body breaks down a drug it produces new chemicals, called metabolites, which may have psychoactive effects similar to the parent drug though some are also toxic. The half-life (t½) is the time it takes to reduce blood levels by half: the half-life rule applies to most but not all drugs and notably not alcohol. For drugs with short half-lives it is often the metabolite, not the parent drug, that is detected. As a rule of thumb it takes 4-5 half-lives for a drug or a metabolite to be eliminated. The graphics show how heroin, cocaine, and methadone are broken down in the body.
Urine samples are vulnerable to tampering and steps should be taken to ensure the sample is genuine. Drug testing offers qualitative or semi-quantitative reflections of substance use. If practitioners and their clients have a good working relationship there is pretty good agreement (60-90%) between urine testing and self-report of drug use; however, there may be circumstances where a person sees that it is in their interests to conceal their actual drug use. Examples would be child care concerns, high risk occupations, court orders or risk of a prescription being stopped. So, there are times when an objective test is needed in addition to self report.
There are a number of factors influencing detection rates:
Nature of the drug – how is it spread across body fluids
Nature of the drug - how quickly does the body eliminate it
How was the drug taken - injected, smoked, by mouth
The sample under test – saliva, urine, hair
Individual variation
The analytical method used
Where drug screening is used as a primary outcome measure for research or to monitor high risk situations, the frequency of testing and the expected substance use detection rates need to be stated. In order to avoid false positives, that is reporting a drug to be present when it was not, there are national agreements on how much drug must be detected before declaring a positive result and so a certain amount of under-reporting is built into screening tests.
Alcohol behaves somewhat differently to most drugs in that its rate of elimination is constant as shown in the chart. Individuals who are regular drinkers will metabolise alcohol more quickly as a result of enzyme induction.
effective interventions…
