Testing for drugs of abuse usually occurs in two circumstances: possible or known overdose or testing of clinically well persons to detect drug use. Overdose will be discussed in the section on toxicology. Drug screening has its own unique problems. For example, it is necessary to provide legal chain of custody protection to specimens so that each time a specimen changes hands the person receiving it documents this fact and thereby becomes the theoretical protector of the specimen. Another difficulty is attempts by some patients to invalidate the tests if the tests are performed on urine. This may involve diluting the urine specimen, adding substances that might interfere with the test, or substituting someone else’s specimen. Possible dilution can be suspected or detected by specimen appearance (appearance suggesting water), very low specific gravity, or specimen temperature less than or more than body temperature. One investigator has found normal urine temperature immediately after voiding to be 97°-100°F (36°-38°C); the National Institute of Drug Abuse (NIDA) current guidelines are 90.5°-99.8°F (32.5°-37.7°C). Addition of foreign substances may be detected by unusual color or other appearance, low specimen temperature, or by unusually low or high specimen pH (normal urine pH is generally considered to be 4.5-8.0). Sometimes there may be an unusual smell. Specimen substitution by the patient may be suspected by specimen temperature lower than body temperature. A fluid without creatinine is probably not urine. Patient identity should be verified, by photograph if possible, to prevent a substitute from providing the specimen.

A variety of methods can be used for initial screening. Currently, the two most popular are thin-layer chromatography (TLC) and some form of immunoassay. The Syva Company EMIT immunoassay was one of the first to be introduced and remains the most popular. Due to the possibility of cross-reacting substances and the implications of a positive test result to the patient, as well as legal considerations, positive screening test results should be confirmed by a method that uses a different detection principle. Currently, the method of choice is gas chromatography followed by mass spectrometry (GC/MS). Instruments are available that combine both components. Gas chromatography separates the various substances in the mixture and the mass spectrometer bombards each substance from the chromatographic separation with electrons to ionize the constituents. The constituents are separated on the basis of mass/charge ratio, and a mass spectrum peak is calculated for each by comparing the mass to the number of ions of that mass that are present. The spectrum peak is a fingerprint that identifies the compound. Therefore, the gas chromatography element separates the constituents, and the mass spectrometry component identifies them.

Marijuana (cannabis). The most important active component of marijuana is d-9-tetra hydro cannabinol (d-9-THC, usually, although incorrect technically, abbreviated as THC). After inhalation of marijuana, THC can be detected in blood in about 1-2 minutes and reaches a peak in about 7 minutes. The sensation attributed to THC, however, does not appear until about 20-30 minutes after the serum peak, at a time when the serum level of THC is considerably lower. It is fat soluble and is quickly deposited into many tissues, including the brain. At the same time, the THC that reaches the liver is metabolized to a compound with psychogenic properties called “11-hydroxy-THC,” which then itself is rapidly metabolized to various compounds, the principle metabolite being a nonpsychogenic water-soluble compound conjugated to glucuronide molecules called “carboxy-THC.” About 30 minutes after absorption into tissues, THC is slowly released back into the blood, where liver metabolism continually reduces its body availability. If more marijuana is smoked before the previous amount has been eliminated, more THC will be deposited in tissues (up to a saturation point), and total elimination takes longer. Shortly after reaching the serum peak, the serum level of THC begins to fall due to tissue absorption and liver metabolism even if smoking continues, reaching only 10% of the peak levels in 1-2 hours. The serum half-life of THC after inhalation is about 0.5-1.5 hours. Carboxy-THC reaches a serum peak at about 20-30 minutes, at which time it begins to exceed THC. At 1 hour after inhalation, about 15% of plasma cannabinoids is THC and about 40% is carboxy-THC. Both THC and carboxy-THC are nearly all bound to plasma proteins (predominantly lipoproteins), and their concentration in plasma is about twice that of whole blood. About two thirds of the cannabinoid metabolites are excreted in feces and about one third in urine. The body elimination half-life of THC is about 24 hours (range, 18-30 hours), and the elimination half-life of carboxy-THC, the principle metabolite, is 3-6 days. Since the elimination half-life of THC is about 1 day and since steady state is reached after five half-lives, if the individual smokes roughly the same number of marijuana cigarettes each day, there will be equilibrium between intake and elimination of THC in about 5 days. Carboxy-THC has a longer elimination half-life, so that constant or heavy use of marijuana greatly prolongs the time that carboxy-THC will be detectable in the urine. Marijuana can be eaten as well as smoked. Absorption from the GI tract is slower and less predictable than through the lungs. Onset of the psychogenic effect occurs about 1-3 hours after ingestion of marijuana. Serum levels of 11-hydroxy-THC are considerably higher after oral intake of cannabis than levels after smoking.

Urine assay. Carboxy-THC is the major metabolite of THC and is the one usually assayed in urine. Length of detectable urinary excretion varies with the amount of marijuana used per day, which, in turn, depends on the type of material (e.g., ordinary marijuana, hashish, or other forms) and the number of times per day of administration. There is also some effect from the route of use (smoking or ingestion) and individual tolerance or variation in the rate of metabolism. There are also assay technical factors. Most investigation of urine carboxy-THC detection has used detection cutoff levels of either 20 ng/ml or 100 ng/ml. The 100 ng/ml cutoff point was used in order to prevent claims that inhaling smoke from someone else’s marijuana cigarette might produce a positive urine test result. Actually, several studies have tested persons exposed to prolonged inhalation from cigarettes of other persons in small, confined areas (severe passive inhalation), and found that only a few persons had positive urine tests at the 20 ng/ml cutoff level. The longest time interval for a positive test was 3 days. Under ordinary experimental conditions of passive exposure, only a few individuals had detectable urine levels at the 20 ng/ml cutoff; detectability usually disappeared in less than 24 hours and almost always by 48 hours. Urine specimens should be frozen if testing is delayed, to preserve carboxy-THC values.

Saliva assay. It has been reported that THC remains in saliva up to 5 hours after cannabis inhalation. Therefore, detection of THC in saliva theoretically might indicate recent use of marijuana. To date, saliva assay has not been widely used.

Time period after use that marijuana presence can be detected. After a single cigarette containing usual amounts of THC is smoked, urine levels become detectable after about 1 hour and remain detectable at the 100 ng/ml cutoff level for 1-3 days and at the 20 ng/ml cutoff level for 2-7 days (therefore, the total detectable time period at the 20 ng/ml level is about 5-7 days, with a range of 2-10 days). For example, in one study those patients tested after smoking a single cigarette showed urine results more than 100 ng/ml for up to 3 days and results more than 20 ng/ml for an additional 5-8 days. Smoking more than one cigarette on the same day for 1 day only extends the detectability time about 2 days. In chronic heavy users, after smoking is stopped, urine results can remain positive at the 20 ng/ml level in some individuals up to 30-40 days. In one report, chronic marijuana users with recent heavy intake had urine assays more than 100 ng/ml for 7-14 days, followed by assays greater than 20 ng/ml for an additional 7-14 days. However, in another study of chronic marijuana smokers, results of about 25% of those who had smoked within 2 days of testing were negative at the 100 ng/ml level.

Interpretation of test results. Carboxy-THC is not psychotropically active, and because of the variability of excretion due to the different factors just noted, detection of this substance in urine (if confirmed) indicates only that the patient has used marijuana in the recent past without providing evidence that correlates with physical or mental effects of marijuana. Serum levels of THC greater than 2 ng/ml is thought to indicate probability that an individual would have some undesirable effects. In some circumstances, such as patient actions that may have been influenced by marijuana, it might be useful to obtain a THC serum level immediately as an indicator of current status and to compare with the urine carboxy-THC level. If the question arises whether marijuana use is ongoing, monitoring the urine periodically (e.g., every 4-5 days) should demonstrate a progressive downward trend in the values if smoking has indeed stopped, although there may be some fluctuations during this time. Initially positive test results with any screening procedure must be verified by a confirmatory procedure (such as GC/MS) if the positive results will lead to some significant action. The different sensitivity levels of different tests must also be kept in mind, as well as the effect of urine concentration or dilution.

Cocaine. Cocaine can be self-administered intranasally, by smoking, or intravenously. It may also be taken orally, but this is not common since gastric juice inactivates most of the drug. Intranasal administration produces peak blood levels in 30-40 minutes (range, 15-60 minutes). About 80% of the dose reaches the bloodstream. Intravenous administration produces peak levels in 3-5 minutes. Smoking pharmacokinetics are similar to those of IV use, with peak levels reached in about 5 minutes, although only an average of about 45% of the dose reaches the bloodstream. The most common form used for smoking is known as “free-base,” which is derived from the active ingredient cocaine hydrochloride by separating the cocaine base from the hydrochloride ions, usually by extracting the cocaine base in a solvent. Already-processed cocaine base is often called “crack.” This is the most potent form of cocaine. Cocaine is very lipophilic and is rapidly taken up by tissues containing lipid, such as the brain. The half-life of cocaine in the body after the serum peak is about 1.5 hours (range, 0.5-2 hours) for all methods of drug intake. About 25%-40% of the dose that reaches the bloodstream is converted to the major metabolite benzoylecgonine by hydrolysis in fluids and peripheral tissues and excreted in the urine. Benzoylecgonine has a body half-life of 7-9 hours, which is about 6 times as long as that of cocaine. About 20%-25% of serum cocaine is converted to other metabolites, with roughly equal contribution by the liver and by serum cholinesterase. About 1% is excreted unchanged in the urine.

Detection of cocaine. Cocaine or its metabolites can be measured in serum or in urine. The serum half-life of cocaine is short, and cocaine from a single dose is usually nondetectable in 6-10 hours, although it may be detectable longer with very sensitive methodology. Multiple doses may prolong serum detectability. Cocaine in urine is detectable for only about 8-12 hours after a single dose. Cocaine is usually investigated in urine through detection of its metabolite benzoylecgonine. This is detectable in urine beginning 1-4 hours after a cocaine dose. How long it will remain detectable depends on the quantity ingested, whether dosage is single or multiple, individual patient variation, and the sensitivity of the detection method. RIA is the most sensitive of the screening methods (5 µg/L) and may detect cocaine metabolites as long as 7 days after a large dose. Enzyme immunoassay (EIA, an EMIT variant) is less sensitive (300 µg/L) and would detect the presence of the same dose for about 2-3 days. Since some false positive results can be obtained with any of the screening tests, a positive result must be verified by a confirmatory method such as GC/MS. The screening methods are designed to detect benzoylecgonine, which remains detectable considerably longer than cocaine, so that a positive urine screening test result does not mean the patient was under the influence of cocaine at the time he or she produced the urine specimen, and the result usually will not predict (except as an estimate involving considerable time variation) when the last dose was taken. Proof of use at a specific time requires detection of cocaine itself in serum or other body tissue. This is usually done by GC/MS. Specimens should be placed in ice and the serum frozen to prevent hydrolysis of cocaine to its metabolites.

Phencyclidine. Phencyclidine (PCP) effects are frequently not recognized; in one study, only 29% of patients were correctly diagnosed on admission. PCP is a water-soluble powder that is administered by smoking water-dissolved drug applied to some smoking material or by ingestion. About 70% of the dose reaches the bloodstream by either route. Peak serum levels are reached 5-15 minutes after smoking. Peak levels after oral intake are reached after about 2 hours. The body half-life of PCP after serum peak levels are reached varies considerably, averaging about 18 hours with a range of 8-55 hours, and are somewhat dependent on the dose. About 10% of the dose is excreted in the urine unchanged, and the remainder as various metabolites without one of them being greatly predominant. PCP or its metabolites are often detected in urine for about 1 week. In some cases it may be detected for several days to several weeks, again depending on the quantity administered, whether administration was acute or chronic, and the sensitivity of the detection method. Drug excretion can be increased by urine acidification. Serum or urine levels do not correlate well with severity of symptoms. PCP or some of its metabolites can be detected by RIA, EIA, TLC, and other techniques. These methods differ in sensitivity and each method has some substances that may cross-react. GC/MS is the best confirmatory method.

Amphetamines. Metamphetamine is used more frequently than the other amphetamines. Amphetamines can be administered orally, intravenously, or by smoking. Tolerance frequently develops, necessitating larger doses to achieve desired effects. Other drugs are frequently used at the same time. Absorption from the GI tract is fairly rapid. Body half-life is 4-24 hours. About half the dose is metabolized in the liver. About 45% of the metamphetamine dose is excreted in urine unchanged, about 5% as amphetamine, and the remainder as other metabolites. Amphetamines are usually detectable in urine by 3 hours after administration of a single dose, and screening test results can be positive for 24-48 hours (dependent to some extent on the size of the dose and the sensitivity of the method). A positive result for amphetamines in urine generally means use in the last 24-48 hours. Screening methods include RIA, EIA, TLC, and other techniques. A substantial number of over-the-counter medications for colds or for weight reduction contain amphetamines or amphetamine analogs that may cross-react in one or more screening tests. Other medications may also interfere. GC/MS is the best confirmatory method.

Morphine and related alkaloids. Morphine and codeine are made from seed pods of the opium poppy. Heroin is made from morphine. Morphine and heroin are usually injected intravenously. About 10% (range 2%-12%) of a morphine dose is excreted unchanged in the urine, and about 60%-80% of the dose is excreted in urine as conjugated glucuronides. The body half-life is 1.7-4.5 hours. Heroin is rapidly metabolized to morphine, with about 7% of the dose excreted as morphine and 50%-60% excreted as conjugated morphine glucuronides. Codeine is excreted primarily as conjugated codeine glucuronides in the urine, but a small amount (<10%) is metabolized to morphine and morphine conjugated glucuronides, which appear in the urine. Poppy seeds are used as a filling for baked goods and also are used unprocessed; they are sold legally even though they contain some natural morphine and codeine. The amount of opiate alkaloids in poppy seeds is not sufficient to produce any symptoms or noticeable sensation, but consumption of a moderate amount of this material can result in detectable concentrations of morphine in the urine that can last as long as 36-60 hours.

Screening tests for morphine and other opiates are similar to those for other drugs of abuse: RIA, EIA (EMIT and others), TLC, and in addition a hemagglutination inhibition assay. Most of these methods cannot differentiate between codeine and morphine. Also, since codeine metabolism results in a small but measurable amount of morphine conjugates, prescription medications containing codeine for pain relief or cough suppressive effects may produce positive test results for morphine. In general, if the concentration of codeine greatly exceeds that of morphine, the parent drug is probably codeine. In general, excluding prescription drugs, the presence of morphine in the urine indicates nonlegal use of morphine, heroin, or codeine in the past 1-2 days. Detection of these compounds should be confirmed, and the compound identified, using GC/MS. In addition, GC/MS can differentiate between poppy seed ingestion and heroin intake by detecting and measuring 6-monoacetylmorphine, a metabolite of heroin that is not present in poppy seeds or in the urine of persons who ingest poppy seeds.