Laboratory Testing

Key Points

• Any drug testing method involves several important considerations:

• Samples can be adulterated to mask true results: creatinine, pH, specific gravity, and temperature are often used to detect urine sample adulteration.

• A single test result is a marker of use at one point in time and does not itself make a diagnosis of abuse or dependence; laboratory detection of drug use is one tool that may be used during screening, diagnosis, treatment, and relapse prevention of substance use disorders.

• Rates of false positives and false negatives depend on the drug ingested, quantity ingested, duration of use, and specific laboratory cutoffs used; it is important to know the cutoff values of the laboratory used and to obtain a comprehensive history of drug ingestion quantity and frequency over time.

Laboratory testing is frequently used in SUD screening, treatment, and monitoring for relapse. The most common testing method is the urine drug test. Other options include blood,

Table 51-4 Drug-Testing Methods: Advantages and Disadvantages

Test

Advantages

Disadvantages

Blood

Difficult to adulterate; detects very recent ingestion

Invasive; drugs clear blood more quickly after ingestion than urine

Hair

Noninvasive; difficult to adulterate; detects patterns of use over time; frequently used in forensics and research

Not useful for recent ingestion; more difficult to process than other methods

Oral fluids

Noninvasive; direct observation easy and makes adulteration more difficult; detects recent ingestion; rapid results

Unintentional contamination from recently ingested substances; drugs clear quickly after ingestion (see Urine)

Sweat

Noninvasive; uses patch for collection; monitor for use over extended period

Quantification of drug levels difficult

Urine

Noninvasive; rapid results; relatively inexpensive vs. other methods

Easy to adulterate sample, even when observed collection method used

sweat, hair, and oral fluid testing. Table 51-4 lists the advantages and disadvantages of each method (Ries et al., 2009).

Table 51-5 details typical detection times and causes of false-positive results for drugs that can be detected by readily available urine drug testing. Most urine drug tests use immunoassays because these are inexpensive, fast, and easily automated. Gas chromatography with mass spectroscopy (GC/ MS) is typically reserved for confirmation of a positive result. Methadone is not a part of most urine drug screen panels and does not show as a positive opiate test. Separate testing for methadone is available. Separate testing is also needed for most "club drugs," including 3,4-methylenedioxymeth-amphetamine (MDMA), ketamine, and y-hydroxybutyrate (GHB). Benzodiazepines have a wide range of potencies, half-lives, and metabolites, which makes urine drug screen results less reliable (Ries et al., 2009).

Table 51-5 Urine Drug Testing: Detection Times and Drugs Causing False Positives

Drug

Detection Time

False-Positive Result

Amphetamines, methamphetamine

1-3 days

Bupropion, chloroquine, chlorpromazine, ephedrine, labetalol, phenylpropanolamine, propranolol, pseudoephedrine, ranitidine, selegiline, trazodone, tyramine, Vick's inhaler

Barbiturates

Short acting: 1-4 days Long acting: several wks

Phenytoin

Benzodiazepines

Highly variable

Oxaprozin, sertraline

Cocaine

3 days

None

LSD

2-5 days

Amitriptyline, chlorpromazine, doxepin, fluoxetine, haloperidol, metoclopramide, risperidone, sertraline, thioridazine, verapamil

Marijuana (THC)

Single joint: 2 days Heavy use: 27 days

Efavirenz, pantoprazole, quinaprine

Methadone

2-3 days

Quetiapine

Opiates

1-2 days

Gatifloxacin, levofloxacin, ofloxacin, papaverine, rifampicin, poppy seeds

Phencyclidine

7 days

Dextromethorphan, diphenylhydramine, thioridazine, venlafaxine

Propoxyphene

6 hours to 2 days

Cyclobenzaprine, diphenylhydramine, doxylamine, imipramine, methadone

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