From the Guidelines
Quantitative drug screen results do not provide information on impairment. This is because drug levels in blood, urine, or other specimens only indicate the presence and amount of a substance in the body, but cannot directly measure how that substance affects a person's cognitive or physical functioning, as noted in a study published in the Annals of Emergency Medicine 1. Impairment depends on many factors beyond just drug concentration, including individual tolerance, metabolism, concurrent medications, underlying health conditions, and the timing of drug use.
Key Points to Consider
- Drug screens often detect metabolites that may be present long after the impairing effects have worn off, which can lead to misleading conclusions about a person's current level of impairment.
- A person's tolerance to a substance, such as opioids or benzodiazepines, can significantly influence the level of impairment associated with a given drug concentration, as highlighted by the lack of correlation between drug screen results and clinical presentation in patients with psychiatric complaints 1.
- Clinical evaluation, including physical examination, cognitive testing, and behavioral observation, is essential to accurately assess impairment and should supplement any laboratory findings.
Clinical Implications
In clinical practice, relying solely on quantitative drug screen results to determine impairment can lead to inaccurate assessments and potentially harmful decisions. For instance, a patient with a high drug concentration but minimal impairment might be unnecessarily detained or treated, while another with lower concentrations but significant impairment might be discharged prematurely.
Evidence-Based Recommendation
Given the limitations of drug screens in assessing impairment, clinical evaluation should always be the primary method for determining a person's level of impairment, with laboratory results used as supplementary information to guide further assessment and management, as suggested by the absence of evidence supporting the routine use of urine toxicologic screens in patients with psychiatric complaints 1.
From the Research
Quantitative Drug Screen Results and Impathing Information
- Quantitative drug screen results provide information on the presence and concentration of a drug in a biological sample, but they do not directly measure impairment 2.
- Impathing information is not directly provided by quantitative drug screen results, as drug-testing techniques are not sophisticated enough to measure impairment from drug use 2.
- The interpretation of drug screening results should be done with caution, considering pharmacological properties and the presence or absence of the parent drug and its metabolites 3.
Limitations of Drug Testing
- Drug-testing methods have limitations, including the inability to determine the route of drug administration, quantity or frequency, as well as when the drug was taken, based on laboratory results 2.
- Selection of the drug to be tested should depend on the local availability of the drug, its abuse potential and clinical effects, as well as on the availability of analytical technology and expertise in testing and in interpreting laboratory results 2.
Clinical Interpretation of Drug Testing Results
- Quantitative urinary results can assist in differentiating "new" drug use from "previous" (historical) drug use, and "spikes" in urinary concentration can assist in identifying patterns of drug use 3.
- Therapeutic drug monitoring (TDM) coupled with pharmacokinetics (PKs) can assist in interpreting the effects of phenoconversion and should be considered for treatment medications/drugs used to manage pain and treat substance abuse 3.
- Clinical interpretation of drug testing results should be done with caution, considering the potential for incorrect test results due to interfering substances or adulteration of the urine sample 2.