Broadly defined, drug testing is the process of using a biological sample to detect the presence or absence of a drug or its metabolites. This process can be completed in a variety of settings and with a variety of techniques. As the body metabolizes various drugs at different rates, the time frame for detecting certain drugs or metabolites can be very specific and can vary widely from substance to substance. Despite the drawbacks, drug testing plays an essential role in the clinical setting because clinical examination, patient self-reporting, and collateral reporting will often underestimate the actual incidence of substance use. However, drug testing should always be used with history/physical and psychosocial assessment.
Although drug testing can be used to confirm the recent use of a substance, it also has a role in the diagnosis, treatment, and monitoring of addiction. As a tool for monitoring, this type of testing has the potential to measure the performance of a patient’s substance use treatment. Urine drug testing (UDT) remains the most common modality for detecting drugs in the human body, and it is based on immunoassay techniques. However, matrices including sweat, hair, nails, blood, breath, and saliva can also be used. Clinicians should understand the value of random drug testing as opposed to scheduled testing, particularly in the context of a suspected or established substance use disorder.
There are several factors that need to be considered when choosing a particular drug test. Using a certain matrix or rotating matrices can reduce the chances of sample tampering. There are also times when a certain matrix may not be appropriate (i.e., using a hair sample with chemically treated hair or using directly observed urine testing in when a patient has had sexual trauma). There is also often a tradeoff when choosing one test over another. Some tests may be regarded as “presumptive” while others are regarded as “definitive." Presumptive tests will typically give a faster result, which may aid in timely clinical decision-making. However, the specificity and/or sensitivity may be lower compared to a definitive test. There may be times when the patient will dispute the results of a presumptive test and a more definitive test can then be done to provide clarification. A clinician may consider going directly to definitive testing if there is no reasonable presumptive test or if the results of the testing will have major implications.
Urine testing typically has a detection window of hours to days. It usually takes two hours before a substance can be detected in the urine. Factors like urine pH and fluid intake can have an impact on the results. Urine is the most well-established matrix and is the most commonly used matrix for point of care testing (POCT). Although sample tampering may be an issue, clinicians have the option of having observed sample collection in many cases. However, this may not completely remove the possibility of sample tampering. One common form of tampering of which clinicians should be aware is dilution. Substances that are likely to be tested for with a urine sample include alcohol, amphetamines, benzodiazepines, opiates/opioids, cocaine, and cannabis.
Blood testing is primarily done in emergency situations and is typically used to detect ethanol levels. The advantage of blood testing is that it allows for a precise level to be assessed. The downside includes the invasiveness of the test, the need for someone skilled to obtain the sample, and the fact that the sample can be a potential biohazard.
Breath testing is also primarily used for alcohol detection. More precisely, it allows for assessment of recent alcohol use. The result is called a breath alcohol concentration or BrAC. The BrAC is often used as an estimate of blood alcohol concentration (BAC). However, on an individual basis, the BrAC can either overestimate or underestimate the blood ethanol level. Research has been focusing on the potential use of breath testing for the detection of cocaine, cannabis, benzodiazepines, amphetamines, opioids, methadone, and buprenorphine.
Oral fluid testing (OFT) generally detects concentration that correlates with plasma concentrations. However, the concentration of orally consumed substances will be higher. Oral testing is more likely to detect parent compounds versus urine testing which relies more heavily on metabolite concentrations. One study looked at the preference of OFT versus UDT in a forensic psychiatry population. Both patients and staff were found to prefer OFT which helped to maintain dignity and save the time of staff, despite the extra monetary cost.
Sweat testing is completed through the use of an absorbent pad that is collected. The results of testing this pad give a cumulative concentration that suggests how much of a substance that person consumed over the entire period that the pad was worn. There can be problems with contamination or incomplete adhesion of the patch to the skin. One benefit of sweat testing is that it gives a detection window of hours to weeks.
Hair, as a matrix for the detection of substances, can provide information on cumulative substance use. Similarly to sweat testing, hair testing has a long detection window. Scalp hair has a detection window of three months, while slower-growing body hair has a detection window of up to 12 months. The results of the hair testing can vary based on the individual in regards to characteristics of their hair. Hair testing can be used the detection of cocaine, phencyclidine (PCP), amphetamines, opioids, and 3,4-Methylenedioxymethamphetamine (MDMA).
Often, contingency management is paired with drug testing in the treatment of addiction and behavioral incentives are allowed on the basis of a negative result. These incentives (or “reinforcers”) can be vouchers or prizes that are given to encourage the patient to continue in their abstinence from a particular substance. The use of POC testing, in particular, makes implementation of contingency management easier because of the rapid results that can be achieved.
The technologies behind drug testing as well as the clinical application of this technology are rapidly evolving. It is important that clinicians understand the proper use of current methods and stay informed about emerging techniques. One of the biggest challenges facing clinicians is the accurate detection of drugs that have relevance to clinical outcomes. Another concerning issue is that some substances are so new that tests have not been developed to detect their presence accurately. Additionally, some synthetic drugs are designed not to produce a positive result on a drug screen. More research should be done to address sample tampering and continuing research and development need to keep pace with new substances. Another area of concern is the issue of drug testing adolescents. In particular, the American Academy of Pediatrics Committee on Substance Abuse has made it clear that involuntary drug testing of an adolescent with decisional capacity is inappropriate.
A positive result on a drug test tells the clinician that the patient had a detectable amount of a substance present during a certain window of time. This result does not typically indicate that impairment is the result of any particular substance or that the patient has a substance use disorder. A major consideration when using drug testing is regarding the significance of a negative result. Clinicians should bear in mind that a negative result simply means that the particular substance could not be detected. This may mean its level was not sufficient enough to be detected or that use of that substance did not occur during the detection window. It does not, however, rule out substance use or a substance use disorder. It is essential that clinicians understand the sensitivity, specificity, false negative results, and false positive results. For example, false negative immunoassay results for cocaine and benzodiazepines were fairly common when compared to mass spectrometry analysis.
Another issue regarding the use of drug testing in the clinical setting is the attitude by some patients that the results of a drug test may be used in a punitive way. It is important that patients understand the role drug testing will play in supporting their recovery and that it will not be used as a tool to implicate them in a crime or reprimand them.