Drug Testing

Specimen Selection and Timing of Collection

Specimens

Urine and blood (whole blood, serum, or plasma) tests are available to detect most drugs commonly prescribed for pain management and other legitimate indications, as well as many nonprescribed substances. Urine is typically preferred for screening, adherence, and drug exposure testing; blood is an acceptable alternative. ^,  There is no evidence that drug testing in alternative specimens (eg, hair, saliva) is more effective than urine testing for monitoring adherence, such as in the management of patients with chronic noncancer pain.  Refer to the ARUP Consult Drug Half-Lives and Urine Detection Windows topic for more information about when drugs may be detectable in plasma and urine specimens.

Timing of Collection

Specimens should be collected for drug testing based on the clinical scenario and routine practices. For example, specimens may be collected for testing when qualifying patients for chronic therapy with opioids or other controlled substances, when enrolling patients in substance misuse disorder programs, in situations when aberrant drug behavior is suspected, and in patients who are pregnant. This testing is intended to confirm the presence of prescribed medications that are detected by the test and to detect the presence of illicit and nonprescribed drugs.  Refer to the ARUP Consult Drug Half-Lives and Urine Detection Windows topic for more information about when drugs may be detectable in plasma and urine specimens.

Commonly Used Testing Strategies

Laboratory drug testing approaches are unique in terms of performance characteristics, and the strategy for testing should align with the goals of testing. Testing strategy choices include screening only, screening with definitive confirmation, and first-line definitive testing.

Screening tests are generally sensitive for substances of interest but may not be highly specific.  Screening may be useful to quickly evaluate whether a drug is present in a variety of contexts. For example, random screening is recommended one or more times annually in individuals prescribed controlled substances for pain management.  Screening is also commonly performed during pregnancy, as part of an acute care or emergency visit when intoxication or exposure is suspected, and for regular monitoring in patients taking psychiatric medications or with substance use disorder. Drug screening may also be performed as part of a preemployment check. Screening may be performed in many matrices, although urine is the most common specimen for screening tests. Initial screening methodologies often include point-of-care (POC) screening devices (eg, urine cups) and laboratory immunoassays, although mass spectrometry may sometimes be used.

Confirmatory or first-line definitive testing is generally recommended if significant action or a change in clinical management depends on results. Confirmatory testing is also recommended when any presumptive test yields a result that is not consistent with the clinical expectations, for opiates/oxycodone and/or benzodiazepines (regardless of the screen result) if the patient is prescribed those drugs,  and for amphetamines due to the number of substances that may yield false-positive results. Confirmatory testing is performed using a highly specific definitive testing technique (eg, mass spectrometry) on either urine or blood, and may be quantitative or qualitative.  Individually orderable targeted tests for specific drugs or drug classes are useful for confirming results, when presumptive tests are not available to detect the drug(s) of interest, or when only select drugs or drug classes are of interest.

Immunoassays are commonly used for first-line screening and may be qualitative or semiquantitative. Immunoassays may have several advantages, including ease of use, fast turnaround time, and lower cost; however, immunoassays may have lower sensitivity and specificity than other methods and can produce false-positive and false-negative results. ^,  Many different substances can contribute to false-positive immunoassay screen results. Whether or not a particular substance will interfere with an immunoassay may be assay-, patient-, and substrate-specific. For example, benzodiazepine immunoassays may not be able to distinguish between similar drugs such as alprazolam, clonazepam, and lorazepam.  Therefore, immunoassay results should be considered as presumptive only, and confirmation by mass spectrometry is generally recommended if significant action or a change in clinical management depends on results.

Although mass spectrometry may be used for screening, it is generally used for confirmation of immunoassay screening results or for monitoring in specific clinical situations. Mass spectrometry is considered definitive and is the gold standard for confirmatory testing. Although liquid chromatography-mass spectrometry (LC-MS) is most commonly used, gas chromatography-mass spectrometry (GC-MS) is still used in some applications. Tandem mass spectrometry (MS/MS) increases the specificity of the assay. Because mass spectrometry is often a targeted method, only the specified analytes of interest will be detected; other analytes may be present but not reported (eg, analogs, cutting agents, novel psychoactive substances). Discussion with the laboratory to ensure all substances of interest are detected is advised.

Mass spectrometry allows simultaneous monitoring of the parent substance and its metabolites within the same sample, which can clarify which substance (or substances) was taken. It is therefore very important to understand the metabolic pathways of the substances of interest. For example, monitoring diazepam, nordiazepam, temazepam, and oxazepam can clarify which of these benzodiazepines was present (refer to the Benzodiazepine Metabolism diagram). As another example, mass spectrometry can distinguish between poppy seed and heroin consumption (refer to the Opiates and Opioid Metabolism diagram).

Testing Considerations

Immunoassays for Specific Drug Classes

Immunoassay screening may be for an entire class of drugs or for an individual analyte; there are specific considerations for particular drug classes when screened by immunoassay.

Opiate/Opioid Immunoassays

Many available opiate immunoassays do not readily detect semisynthetic opioids (eg, oxycodone) and synthetic opioids (eg, fentanyl, methadone, meperidine, tramadol). False-negative results may occur with tests that screen for multiple opiates because individual drugs may not react as well (or at all) with the test. Furthermore, immunoassay results may be positive due to a variety of taken substances that have the same metabolites (eg, both heroin and prescription hydrocodone may cause a positive result in a class-based screen); refer to the Opiates and Opioid Metabolism diagram for more information. It is recommended that all immunoassay screen results for opiates/opioids be confirmed by a definitive methodology if a clinical decision is to be made based on drug testing results.

Benzodiazepine Immunoassays

Many drugs belong to the benzodiazepines group, and an assay’s ability to detect them varies based on assay formulation and cutoff limit. False-negative results may occur because individual benzodiazepines may not react as well (or at all) with the assay. Most benzodiazepines are metabolized and conjugated before elimination through urine. Therefore, the ability of an immunoassay to detect respective metabolites also contributes to its apparent sensitivity to detect certain drugs. Most immunoassays do not detect designer benzodiazepines. Many benzodiazepines share a common metabolic pathway; refer to the Benzodiazepine Metabolism diagram. It is recommended that all immunoassay screen results for benzodiazepines be confirmed by a definitive methodology if a clinical decision is to be made based on drug testing results.

Amphetamine and Methamphetamine Immunoassays

Urine immunoassays are designed to detect the d-isomer (psychoactive compound) of amphetamine and methamphetamine, with limited detection of the l-isomer. Nevertheless, most immunoassays do not perform well in the detection of other synthetic central nervous system (CNS) stimulants, including phentermine (moderate sensitivity), methylphenidate, methylenedioxyethylamphetamine (MDEA), methylenedioxymethamphetamine (MDMA), and methylenedioxyamphetamine (MDA). Immunoassays for amphetamines and methamphetamines may produce high false-positive result rates due to a variety of different substances.  It is recommended that all immunoassay screen results for amphetamines be confirmed by a definitive methodology if a clinical decision is to be made based on drug testing results.

Cannabinoid Immunoassays

Cannabinoids, including THC, are substances that can interact with cannabinoid receptors. There are hundreds of cannabinoids present in plants, as well as many synthetic cannabinoids. Delta-9-THC may be the primary cannabinoid substrate of interest in drug screening immunoassays; however, other cannabinoids (eg, delta-8-THC and cannabidiol) may cross-react in these tests. Synthetic cannabinoids may not be detectable in immunoassays, which presents a clinical and laboratory challenge due to the continued emergence of novel drugs.

Cocaine Immunoassays

Benzoylecgonine is the primary metabolite detected by urine immunoassays for cocaine; the parent substance is generally not detected. Cocaethylene may be monitored for evidence of concurrent cocaine and alcohol use, as it is only produced when both substances are taken together.

Quantitative vs. Qualitative Testing

Quantitative definitive urine testing is not more useful at detecting outcomes in a clinical context compared with qualitative definitive urine testing; quantitative definitive urine testing should not be used to evaluate the dosage of administered drugs or adherence to a prescribed dosage regimen. 

Quantitative definitive urine testing can be used to:

• Identify variant drug metabolism
• Detect pharmaceutical impurities
• Detect metabolism through minor routes 

Test Result Interpretation

Test results may be surprising not only when unexpected positive results are found, but also when expected positives are absent. Refer to the Urine Drug Testing (Unexpected Results) Algorithm for additional information on assessing unexpected results.

Pharmaceutical Impurities

Some drug tests, particularly opioid tests, may have unexpected positive results due to pharmaceutical impurities. Several opioid medications have allowable limits for process impurities, which may be detected by definitive testing methods. There are other types of impurities, and other medications are also subject to process impurities.