Drug confirmation tests
Drug confirmation tests (Forensic Science)
Drug testing can be conducted on a variety of bodily substances (blood, urine, sweat, saliva, or hair) using a variety of tests. After an initial screening test indicates the presence of a banned substance in a person’s body, a follow-up test may be done to verify or disprove the original finding; this second test is known as a drug confirmation test.
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Federal Guidelines (Forensic Science)
In the United States, guidelines for drug testing were established by the Substance Abuse and Mental Health Services Administration (SAMHSA) in September, 1994. According to these guidelines, for every initial screening and confirmation test, a chain of custody must be established and followed in obtaining the specimen. Only authorized persons should handle and transport all specimens, in accord with the chain of custody, and care must be taken to ensure that samples are not diluted (by the addition of water or any other substance). If the result of an initial screening test is negative, no further testing needs to be done. If any specimen yields positive results on an initial screen, however, a confirmatory retest of that specimen must be done.
According to the SAMHSA guidelines, the new test conducted on the initial sample must be completely independent of the initial test and must use a technique that is completely different from that used in the original test. All confirmation tests must be of equal or greater sensitivity than the original test; they should be conducted using gas chromatography or mass spectrometry. Standard cutoff values (confirmatory test levels) have been established on these tests for marijuana, opiates, cocaine, morphine, codeine, phencyclidine (PCP), amphetamines, and methamphetamine. Any sample that has a test level above the standard cutoff is reported as positive. If a drug confirmation test...
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Substances Commonly Used in Drug Testing (Forensic Science)
Various bodily substances can be analyzed for the presence of drugs or their breakdown products (metabolites). Although blood analysis yields valid and reliable results, it is rarely done because of the invasive nature of blood testing. Urine drug testing (urine toxicology screening) is probably the most commonly used technique, whether for initial screening or confirmation screening. When a urine sample is used in testing for drugs or metabolites, the tester must be sure of the source of the urine (that is, that the person being tested has not substituted someone else’s urine) and must be certain that the sample is pure and undiluted.
Saliva-based drug screens are becoming more widely used, as they are easily done, can be done in the presence of witnesses (thus confirming no substitutions), cannot be altered, and yield valid and reliable results similar to those obtained by urine testing. Drugs and their metabolites can be detected in saliva immediately after drug use and for up to three days following use.
Hair testing has often been used to detect drug use, as it is reasonably accurate and reflects drug use for a period of at least three months prior to testing. Some questions have been raised about false positives on hair tests, however; the different structures of hair among persons of different ethnic groups may increase the likelihood of false positives. Sweat drug screens involve the...
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Effectiveness of Testing Methods (Forensic Science)
Following the collection of samples, all drug testing is done in a laboratory setting. All samples brought into the laboratory are subjected to initial testing, known as the screening test. This testing is normally done by immunoassay, a method that is less sensitive and less expensive than the methods used in confirmation tests. Because the method used in screening tests is not highly sensitive, it is not unusual for these tests to produce false positive results. Any sample that tests positive initially is then subjected to confirmation testing. The methods used in confirmation tests, mass spectrometry and gas chromatography, produce results that are much more accurate than immunoassay, so samples that produced false positives in screening typically have negative results on these confirmation tests.
Reasons for false positives on drug screenings may include laboratory errors, antibiotic use, the use of nonprescription drugs such as ibuprofen or nasal decongestants, and the ingestion of poppy seeds. Even when false positive initial results are shown to be incorrect by the results of more precise confirmation tests, the record of the person tested may remain unfairly tarnished by the initial findings. For this reason, a number of observers have noted the need for increased public understanding of the reliability of the results of drug confirmation tests.
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Further Reading (Forensic Science)
Bahrke, Michael S., and Charles E. Yesalis, eds. Performance-Enhancing Substances in Sport and Exercise. Champaign, Ill.: Human Kinetics, 2002. Discusses the history of athletes’ use and abuse of performance-enhancing drugs. Chapters 27 and 28 address the topic of drug testing in sports.
Jenkins, Amanda J., and Bruce A. Goldberger, eds. On-Site Drug Testing. Totowa, N.J.: Humana Press, 2002. Collection of essays by scientific experts discusses the various devices available for on-site drug testing. Explains each test’s principles and assesses its advantages and disadvantages.
Mieczkowski, Tom, ed. Drug Testing Technology: Assessment of Field Applications. Boca Raton, Fla.: CRC Press, 1999. Collection of essays by contributors from many disciplines compares the various methods used in drug testing.
Mrozek, John. Drug Screen Manual: The Tests, the Technology, the Risks, the Reality. Boulder, Colo.: Paladin Press, 1998. Brief volume focuses on providing information for persons who may be subject to drug testing. Discusses possible inaccuracies in testing, particularly those that result from poor training of those who administer the tests.
Smith, Frederick P., ed. Handbook of forensic Drug Analysis. Burlington, Mass.: Elsevier Academic Press, 2005. Focuses on methods used to detect drugs in the human body. Presents analyses of a number of drugs and discusses...
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