Testing Methodologies

A multitude of methods are available to aid in the detection of drug use in humans. The most common drug testing technologies are listed in Table 4.1. The most popular initial test screen is an enzyme immunoassay (EIA) analysis of a urine sample. If this is positive, a confirmatory gas chromatography-mass spectroscopy (GC-MS) test is performed on the split sample. Given the greater sensitivity of GC-MS over EIA, the cutoff levels are reduced. The most commonly used analytic technique for a "comprehensive drug screen," thin-layer chromatography (TLC), is the least expensive test available. TLC utilizes the differences in polarity and chemical interaction with developing solvents to produce different visualizations on a thin-layer coating. The visualizations are highlighted using ultraviolet (UV) or fluorescent lighting, or by color reactions created after being sprayed with chemical dyes. Identical molecules cluster in the same area, yielding specific color reactions. Unfortunately, TLC is somewhat insensitive to detection of controlled substances.

Of all the available tests, how does a clinician decide on which test to administer? If there is no clinical indication to test for a specific compound, a "comprehensive drug screen" may be performed. There are settings and instances when it is important to contact the laboratory to ensure that there is a means to test for the substance, or to prompt the laboratory to test for the sub-

TABLE 4.1. Most Common Drug Testing Technologies

• Thin-layer chromatography

• Radio immunoassay, enzyme immunoassay, fluorescent polarization immunoassay, enzyme-linked immunosorbent assay

• Gas chromatography

• Gas chromatography-mass spetroscopy

• Liquid chromatography stance. It is common for general hospital laboratories to screen only for a limited number of substances. For example, many do not screen for gamma-hydroxybutyric acid (GHB) (although methods for testing for GHB continue to undergo refinement; Chappell, Meyn, & Ngim, 2004). A drug screen done using TLC will only detect high levels of the following compounds: amphetamine, barbiturates, cocaine, codeine, dextromethorphan, diphenylhydan-toin, morphine, phenylpropanolamine, methadone, propoxyphene, or quinine (a heroin diluent). TLC does not detect the following compounds: 3, 4-methlyenedioxyamphetamine (MDA), 3, 4-methylenedioxymethamphetamine (MDMA), fentanyl, D-lysergic acid diethylamide (LSD), marijuana, mescaline, and phencyclidine (PCP).

Although urine analysis is the most widely used and best overall body fluid to screen for drug use, other body fluids can be measured as well. Hair testing is growing in popularity but is not as sensitive to marijuana use as urine. Despite commercial success, the scientific foundation for using hair analysis is limited. Its primary utility might be as a tool in the diagnosis and treatment of drug abuse disorders, particularly cocaine dependence. Salivary measurements offer the advantage of ease of collection but only detect recent drug use, limiting their utility. A number of drugs, including cocaine, morphine, amphetamine, and ethanol, have been detected in sweat. Unfortunately, there is a wide intersubject variability of drug concentration in sweat. This results in a significant disadvantage when sweat is compared with other body fluids. To add to the problem, sweat collection takes several days to several weeks and requires the use of a sweat patch (Cone, 1996).

For some substances, other tests can be helpful in determining qualitative or quantitative aspects of use. For example, likely alcohol use may be detected by liver enzymes or by the new test for carbohydrate-deficient transferrin (CDT), and some investigators are studying whether certain combinations of these tests have varying specificities or sensitivities (see Chapter 5 on alcohol, this volume). And, certain blood or urine tests are vital in determining the presence of dangerous effects of substances, such as muscle breakdown leading to rhabdomyolysis and a high creatine kinase among users of cocaine and PCP.

For the consultant who works in the "field," requiring on-the-spot testing, a number of kits can be used. Most of these are the "on-site" screening immunoassays. "On-site" testing has a variety of features that make it better suited for companies than its counterpart, TLC. "On-site" testing can produce results in as little as 10 minutes, with significant accuracy. Thus, "on-site" screening is the preferred method outside of the hospital. Despite the popularity of "on-site" kits and the fact that these kits have demonstrated a greater than 97% agreement with GC/MS tests, it must be stressed that these kits provide only preliminary results. For best results, it is recommended that a more thorough analysis on the sample be performed.

Drug Addiction Report

Drug Addiction Report

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