EDUCATIONAL COMMENTARY 2003 3 rd TEST EVENT Chemistry Urine Drug Testing Educational commentary is provided through our affiliation with the American Society for Clinical Pathology (ASCP). To obtain FREE CME/CMLE credits click on the Continuing Education link on the left side of the screen. Learning Outcomes Upon completion of this exercise, the participant will be able to: Compare and discuss clinical and workplace drug testing. List the NIDA 5 drugs and the approximate window of detection of each when the testing follows guidelines for federally regulated samples. Interpret positive and specimen validity testing results for (federally) regulated drug testing specimens. Laboratories may be involved with testing biological samples for the presence of drugs for the diagnosis and monitoring of the overdosed patient (clinical testing) and for workplace drug testing (forensic testing). Even though the purpose of such testing is very different, the same methods are often used for both because of the availability and ease of performance of immunoassays on automated instruments. In the emergency department, physicians initially treat the signs and symptoms of the overdosed patient and rely on the laboratory drug testing results to confirm the diagnosis and to possibly monitor treatment. The National Academy of Clinical Biochemistry (NACB) practice guidelines for the use of laboratory tests to support poisoned patients recommends that the clinical laboratory provide two tiers of drug testing: a first tier of qualitative and quantitative tests available on a stat basis to support evaluation of acute toxicity for specific toxins (Table 1) for which an antidote or specific therapy is available, and a second tier (turnaround time of 24 hours or less) of more comprehensive testing of patients with continuing medical problems from exposure to other drugs and chemicals. The 1988 Mandatory Guidelines for Federal Workplace Drug Testing Programs and subsequent revisions mandate scientific and technical procedures for the drug testing process, including : collection, transportation of specimens, testing procedures incorporating quality control, method evaluation, and results reporting, and standards for laboratory accreditation by the National Laboratory Certification Program (NLCP). Although private-sector industries are not required to follow the guidelines developed for the federal program, many choose to do so. Currently, urine is the specimen of choice for both clinical and workplace drug testing with certain exceptions (i.e., ethanol testing under DOT in which breath, blood, or saliva matrices are acceptable; see Table 1 for clinical samples). Urine offers the advantages of non-invasive collection and a relatively easy, cost-effective proven technology versus the disadvantages of a short window of detection (Table 2) and lack of correlation between concentration and impairment. Guidelines mandate a controlled collection and use of standardized Custody and Control Forms as the specimen requisition, chain of custody, and official report form.
A laboratory may only test for certain drugs (the NIDA 5") at specified cutoff levels for federal workplace drug testing (Table 2). Testing for other drugs (e.g., barbiturates, benzodiazepines, propoxyphene, methaqualone, etc.) and at other cutoff concentrations may occur for non-regulated, regulated, and clinical samples. This article will be limited to a discussion of the NIDA 5 drugs. Regulated testing mandates initial screening by an immunoassay method and subsequent confirmation of all screening-positive samples by gas chromatography mass spectrometry (GCMS). Clinical testing may utilize any combination of methods available. Test Interpretation Testing for amphetamines in regulated samples includes testing for only amphetamine and methamphetamine. Methamphetamine is metabolized to amphetamine, and a positive methamphetamine specimen must contain amphetamine at a concentration greater than 200 ng/ml, in addition to methamphetamine at a concentration of greater than the 500 ng/ml cutoff. Several prescription medications (Adderall, Dexedrine, Didrex, Eldepryl, etc.) contain either amphetamine or methamphetamine or compounds that are metabolized to these substances. For clinical and non-regulated testing the detection of other amphetamine-like substances, such as MDMA (Ecstasy) and sympathomimetic amines (ephedrine, pseudoephedrine, etc.) is often requested. The ability of the laboratory to detect such compounds is dependent on the specificity of the antibody in the immunoassay used for screening. Most of these antibodies have been developed to react with methamphetamine and/or amphetamine and may not detect other similar substances. Screening immunoassays for cannabinoids detect multiple metabolites of marijuana with a cutoff concentration of 50 ng/ml used for regulated drug testing. GCMS confirmation identifies and quantitates the major metabolite, 11-nor-tetrahydrocannabinol-9-carboxylic acid (delta-9 THCA), using a cutoff of 15 ng/ml. Chronic marijuana users may produce positive results for longer periods of time than acute users - up to several weeks - because of accumulation of cannabinoid metabolites in fatty tissue followed by slow release. Studies have shown that it is highly unlikely that a nonsmoking individual could inhale sufficient smoke via passive inhalation to result in a positive result when using a screening cutoff of 50 ng/ml. Immunoassays with cutoffs of 20 ng/ml and 100 ng/ml are available for non-regulated and clinical testing, although NACB guidelines recommend that there is no clinical reason for routine cannabinoids testing in the overdosed patient. Cocaine is rapidly metabolized, and the major metabolite, benzoylecgonine, is the primary compound measured by cocaine (metabolite) immunoassays. There are no cocaine-containing prescription medications, but cocaine solutions are sometimes used as a topical anesthetic for various ear, nose, throat, bronchoscopic, and ophthalmological procedures.
Immunoassays for opiates are designed to detect morphine and/or codeine at the cutoff levels and may or may not detect other opiates (such as hydromorphone, hydrocodone, and oxycodone) based on the specificity of the antibody. Heroin is rapidly metabolized to 6-acetylmorphine (6-AM; 6-MAM) and then to morphine. Poppy seeds contain morphine, and their ingestion may cause a positive opiates result. To eliminate or reduce the number of positive results due to poppy seed ingestion, the opiates cutoff levels for federal workplace testing were changed in December 1998 from 300 ng/ml to 2000 ng/ml, and testing for 6-AM testing is now required when the morphine concentration is greater than > 2000 ng/ml. The presence of 6- AM confirms the use of heroin. Immunoassays for opiates with a cutoff of 300 ng/ml are available and are frequently used for clinical and non-regulated workplace drug testing. There are no legal uses of the hallucinogen phencyclidine (PCP) and no other substances can be misidentified as PCP using GCMS. High concentrations of dextromethorphan have been reported to cause false-positive PCP screening results for some immunoassays. Specimen Integrity In addition to testing for drugs, laboratories are now required to perform specimen validity testing to identify dilute, substituted, or adulterated samples for regulated drug testing. This testing includes creatinine, specific gravity (when the creatinine is <20 mg/dl), ph, and nitrites measurements. Testing for known adulterants, such as glutaraldehyde, pyridinium chlorochromate, or oxidizing chemicals, as a class is optional. Guidelines for testing and reporting (Table 3) have been developed. Regulated samples reported as positive for any drug, substituted, adulterated, and/or invalid, must be retained in secured frozen storage for a minimum of 1 year. Review of Test Results All regulated sample results are reported to Medical Review Officers (MROs), who are physicians that review them and are empowered to determine whether a positive test result has an innocent medical cause, such as a prescribed medication, is forensically and scientifically supportable, and whether or not it identifies the donor as an illegal drug user. In order to aid the MROs and emergency department physicians in the interpretation of drug testing results, laboratorians should be aware of the specificity (i.e., cross-reactivity of antibodies for immunoassays) and sensitivity of all assays that they perform. Suggested Reading 1. Mandatory guidelines for federal workplace drug testing. Federal Register. 1988;53;11970-11989. 2. Mandatory guidelines for federal workplace drug testing. Federal Register. 1994;59;29908-29931. 3. Wu AHB, McKay C, Broussard LA, Hoffman RS, Kwong TC, Moyer TP, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: recommendations for the us e of laboratory tests to support poisoned patients who present to the emergency department. Clin. Chem. 2003;49(3):357-379.
Table 1. List of Recommended Stat Quantitative Serum and Qualitative Urine Assays Required to Support an Emergency Department Quantitative Serum Assays Acetaminophen Lithium Salicylate Theophylline Co-oximetry (O2 saturation, carboxyhemoglobin, methemoglobin) Valproic acid Carbamazepine Phenobarbital (if urine barbiturates is positive) Digoxin Iron Transferrin (or UIBC assay) Ethyl alcohol Methyl alcohol Ethylene glycol Qualitative Urine Assays Cocaine Opiates Barbiturates Tricyclic antidepressants Amphetamines* Propoxyphene* PCP* *Need for these assays may be based on the prevalence of drug use in a region. Source: Wu AHB, McKay C, Broussard LA, Hoffman RS, Kwong TC, Moyer TP, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: recommendations for the use of laboratory tests to support poisoned patients who present to the emergency department. Clin Chem. 2003;49(3):357-379. Table 2. Cutoff Concentrations and Windows of Detection for Federally Regulated Urine Drug Testing Drug(s) Screening Test (ng/ml) Confirmation Test (ng/ml) Approximate Detection Period Amphetamines 1000-2 3 days Amphetamine - 500 - Methamphetam ine - 500* - Cannabinoids 50 15 5 7 days (single use) Cocaine Metabolite(s) 300 150 2 3 days Opiates 2000-3 4 days Codeine - 2000 - Morphine - 2000 - Phencyclidine (PCP) 25 25 3 8 days *must contain amphetamine at a concentration of > 200 ng/ml delta-9-tetrahydrocannabinol-9-carboxylic acid benzoylecgonine test for 6-AM when morphine >2000 ng/ml Source: Broussard, LA. Workplace Drug Testing. ASCP Check Sample, Clinical Chemistry No. CC 03-7. Chicago, IL: ASCP Press; 2003;43(7):108.
Table 3. Reporting Results of Specimen Validity Testing on Regulated Samples Test(s) Results Report As: <20 mg/dl <1.003 Dilute <5.0 mg/dl <1.002 or 1.020 Substituted <5.0 mg/dl on both of two aliquots 1.002 1.020 on either of two aliquots >5.0 mg/dl on either of two aliquots 1.000 on both of two aliquots 5.0 20 mg/dl on either of two aliquots >1.020 on both of two aliquots ph <3.0 or 11.0 Adulterated ph 3.0 4.0 or 10.0 10.9 Nitrites >500 µg/ml Adulterated Source: Broussard, LA. Workplace Drug Testing. ASCP Check Sample, Clinical Chemistry No. CC 03-07. Chicago, IL: ASCP Press; 2003;43(7):112. ASCP 2003