Drug Testing - Monitoring of Drugs

Diagnosis

Indications for Testing

  • Detection of inappropriate drug use, therapeutic drug monitoring (see Monitoring section), or compliance testing (see Monitoring section)

Laboratory Testing

  • Specimen types
    • Urine
      • Commonly used for compliance testing and to identify inappropriate drug use or exposures
      • Time over which a drug can be detected is drug-specific
      • For more information, refer to the Drug Analytes Detected in Plasma and Urine table
    • Serum/plasma
      • Best specimen to correlate physiological signs and symptoms (eg, impairment, toxicity, therapeutic response) with drug use or concentration
      • Also used when urine is unavailable
      • For most drugs, the specific time over which a drug can be detected is shorter than for urine
      • For more information, refer to the Drug Analytes Detected in Plasma and Urine table
    • Meconium/umbilical cord tissue
    • Hair
      • Long-term exposures
      • Most useful at least one month after a suspected drug exposure or for chronic drug exposures
    • Oral fluid
      • Useful for detection of free drug
      • Represents a time frame of drug use or exposure most similar to serum/plasma
  • Testing approach
    • Drug testing may be performed based on a targeted analysis of one or more drug classes, as in the case of therapeutic drug monitoring or confirmatory testing, or based on a qualitative screen that identifies several drug classes
      • Drug screens can be ordered as “screen only” or with reflex to confirmation
        • Any drug class identified in the screen would be confirmed by a targeted assay
      • Targeted screening and comprehensive screening tests covering a range of drug classes are available
      • Meconium testing is not available as “screen only” due to the high rate of false positive results for some analytes
      • Therapeutic drug monitoring tests are listed at http://www.aruplab.com  based on generic name
      • See ARUP Pain Management resource for further information
    • Drug testing may be performed under forensic or non-forensic conditions
      • Forensic
        • Involves a chain of custody
        • Usually performed by a forensic laboratory (eg, blood alcohol testing in an automobile accident or occupational drug testing)
      • Non-forensic
        • Does not involve a chain of custody
        • Usually performed by a clinical laboratory (eg, medical testing)
  • Detection of inappropriate drug use
    • Classic drugs of abuse
      • Five panel drug test [modification of the Substance Abuse and Mental Health Services Administration (SAMHSA) 5] includes the following
        • Amphetamines – amphetamine, methamphetamine, MDMA (ecstasy), MDA, and MDEA
        • Opioids – morphine, codeine, 6-acetylmorphine (heroin metabolite), hydrocodone, hydromorphone, oxycodone, oxymorphone and dihydrocodeine
        • Marijuana metabolite
        • Cocaine metabolite
        • Phencyclidine (PCP)
      • Additional panels include other drug classes
      • Available in urine with or without alcohol testing
    • Extended panels may include the following and are available separately
      • Sedative-hypnotics – benzodiazepines and barbiturates
      • Opioids – buprenorphine, fentanyl, meperidine, methadone, propoxyphene tapentadol, tramadol, and relevant metabolites
      • Stimulants – methylphenidate
      • Tricyclic antidepressants
    • Social drugs, available in extended panels or individually
    • Targeted multi-drug panel for serum/plasma
    • Comprehensive testing for urine or serum/plasma

Monitoring

  • Detection of drugs and the actual concentrations of drugs and drug metabolites depends upon the following
    • Analytical method
      • Cutoff concentrations, sensitivity
      • Drugs included in the test design
      • Specificity
    • Patient
      • Clinical factors (liver, kidney, gastrointestinal issues, pregnancy)
      • Age/sex
      • Co-medications
      • Diet
      • Genetic factors
    • Drug of interest
      • Stability in vitro
      • Formulation(s) used
      • Route of administration
      • Pattern of use
      • Pharmacokinetic factors
    • Specimen
      • Timing of specimen collection relative to drug administration
      • Specimen handling/processing
  • Therapeutic drug monitoring
    • Testing to support a wide variety of therapeutic drugs (eg, anticonvulsants, antidepressants, antipsychotics, antiarrhythmics, immunosuppressants) is available; more details are available from the laboratory performing the test
    • Purpose
      • Compare values at steady-state to published therapeutic targets/ranges or individual patient history to optimize dose
        • Examples of drugs for which therapeutic drug monitoring is observed – anti-epileptics, immunosuppressants, anti-arrhythmics, and antibiotics
      • Evaluate clinical signs and symptoms, failure to respond, and toxicity, particularly for drugs with a narrow therapeutic index
      • Detect drug-drug interactions or variation in pharmacokinetics
      • Evaluate compliance with prescribed therapeutic regime
    • Drug testing may include parent drug, free drug, and/or drug metabolites
    • Best specimen
      • Timed blood or serum/plasma
      • Consult laboratory for drug-specific specimen preservatives and handling instructions
    • Time to collect depends on specific drug, patient characteristics, reason for testing
    • Methods may not be equivalent between labs
  • Compliance testing (eg, pain management)
    • Purpose
      • Assure compliance with prescribed (known) drugs
      • Ensure patients are not taking drugs that are not prescribed (licit or illicit)
    • Best specimen
      • Random urine, unless a patient cannot provide a urine specimen (eg, dialysis patient)
      • Diluted urine will compromise detection
    • Drugs detected, cutoffs and approaches vary between labs
      • Consult with laboratory to align needs and requirements with options

Clinical Background

Drug testing determines the presence or absence of drugs and/or drug metabolites.  Drug testing may be quantitative (particularly useful for therapeutic drug monitoring) or qualitative to verify compliance with prescribed therapy or identify inappropriate drug use.

Definitions of common drug testing terms
Definitions of Drug Testing Terms
Biologic half-lifeTime required for one-half of a substance (eg, a drug) to be lost through biologic processes (eg, distributed, metabolized, eliminated).
Chain of custodyChronological documentation or paper trail showing the collection, custody, control, transfer, processing, analysis, destruction and disposition of evidence (including biological specimens).
Confirmation testSpecific drug test performed after a drug screen to confirm the identity of a drug class, individual parent drug, and/or drug metabolite; confirmatory tests are frequently based on mass spectrometric methods and are often quantitative.
CutoffThreshold concentration for a drug class, specific drug, or drug metabolite above which a specimen is reported as “positive” or “present”; cutoff may be defined by the manufacturer of a commercial kit (eg, immunoassay) or based on the limit of quantitation validated for a laboratory-developed test (eg, mass spectrometry).
Drug screenTest intended to identify the presence or absence of one or more drug classes or specific drugs.
Free drugDrug or drug metabolite not bound to protein or other moieties such as glucuronides; biological activity, transport, and elimination of drugs and drug metabolites is often different for a free versus a bound drug.
ForensicRelating to or dealing with evidence intended for use in a court of law (eg, to support crime and death investigations, workers’ compensation claims, and pre-employment testing).
HydrolysisChemical process of decomposition involving the splitting of a bond and the addition of the hydrogen cation and the hydroxide anion of water.
Common laboratory technique used to dissociate glucuronide and other conjugates of drugs in order to improve detection of many drugs in urine.
Methods that employ hydrolysis prior to analysis are presumed to generate a “total” drug concentration.
Limit of detection (LOD)Concentration at which the target compound can be identified.
Limit of quantification (LOQ)Concentration at which quantitative results can be reported with a high degree of confidence.
MetaboliteAny product of metabolism; metabolites can be pharmacologically or toxicologically active or inactive.
PharmacodynamicsStudy of drug response, particularly the mechanisms associated with the binding and interactions of pharmacologically active molecules at their tissue site(s) of action.
PharmacokineticsStudy of drug liberation, absorption (bioavailability), distribution, metabolism, and elimination over time.
SpecificityLikelihood for detection of a given drug or drug metabolite (ie, likelihood of false-negative and false-positive results).
Total drugTotal protein-bound and free drug identified in a specimen; also the concentration resulting after specimen hydrolysis that is thought to represent the sum of free and conjugated drug.

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Drug screening panels and testing relevant to monitoring pain management patients

Refer to ARUP Pain Management Test Directory

   
Drug tests relevant to all clinical applications

Refer to http://www.aruplab.com for complete list of drug tests