Drug Testing Methods and Analysis

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Drug Testing Methods and Analysis

There are a number of reasons for the use of drug tests. Some drug tests are requested by doctors for medical reasons, others by employers to ensure that employees are not working while under the influence of drugs. Drugs can be detected by testing samples of urine, blood, and other bodily fluids, as well as hair. The following sections explain the various reasons for drug testing, and the types of drug testing methods.

Various means are used to test for the presence of drugs, most involving chemical analysis of urine, blood, hair, sweat, or saliva.

Testing for Medical Reasons

Under many different conditions a physician may need to determine whether a person is using illegal drugs and, if so, what kind. A physician needs this information before deciding how to diagnose and treat a patient. For example, a person showing a reduced degree of alertness may be the victim of an illness or be intoxicated. Through drug testing, a physician can rule out drug intoxication. A series of drug tests on fluid and tissue samples (for example, blood, urine, saliva, and hair) permits the physician to more accurately determine the person's condition and then make appropriate medical decisions regarding the patient's care.

Testing in the Workplace

Another circumstance that may lead to drug testing is behavior in the workplace. Workers receive drug tests for two major reasons: (1) problems with job performance and (2) liability, or risk of a lawsuit due to the worker's actions. An employer may believe that employees involved in drug use are likely to be less productive as a result of their drug intoxication.

Employees using drugs may also pose a potential safety hazard. Under the influence of drugs, a worker may be more likely to make errors that reduce efficiency or lead to workplace accidents. For example, an intoxicated equipment operator may work at a less efficient and accurate pace, and may endanger and even injure other workers because of impairment of perception and clouded judgment. Some research has shown that drug-using workers also take more time off and have a higher rate of accidents in the workplace than employees who do not use drugs.

An employer is also expected, under the law, to act responsibly and exercise due diligence in the course of operating a business. An employer who fails to act in this manner is liable for the conduct of his or her employees. For this reason, employers often require drug testing of workers. Courts have generally supported the right of employers to demand drug tests from workers when it can be shown that there are legitimate concerns about public safety and security.

Testing by the Legal System

The legal system has several different reasons for drug testing. One is to determine whether a criminal offender used drugs, because intoxication is a circumstance that can affect what crime a person is charged with and the punishment that may be given. Society is most familiar with drug testing by law enforcement in the well-accepted and widely used technology of breath analysis to determine the blood alcohol concentration (BAC) of people operating a motor vehicle. It is not only a crime to operate a motor vehicle while intoxicated, but it may be a criminal aggravation of another offense, such as an injury occurring during the course of an accident.

The criminal justice system may also use drug testing to estimate the amount of drug use by persons in their custody, or the general level of drug use in a community. There are several reasons for this. One is that drug use is an illegal behavior that the police are responsible for controlling. Measuring the amount of drug use and how it changes over time is a way to evaluate the effectiveness of drug control policies. Additionally, since convicted offenders are housed in jails and prisons, drug testing among arrestees and convicts can provide critical information to system administrators.

Testing During Drug Treatment and Rehabilitation

Drug treatment and rehabilitation programs rely on drug testing for several reasons. First, it gives a measure of a client's drug use. A second function is monitoring the client for continuing drug use while he or she is participating in treatment. Most treatment programs require abstinence from drug use to remain in treatment.

Another feature of drug testing in treatment programs can be labeled a "self-help" function. Many clients in treatment admit that if they could get away with drug use, they would, but knowing that they will be tested and identified as violators adds an additional motivation for their "staying clean" in treatment. It also provides a reason to refuse drugs that are offered to them in social circumstances. Friends and peers are less likely to offer drugs to a person undergoing drug testing because they fear the drug test will catch that person's drug use.

Finally, drug testing in treatment programs that involve referrals from the criminal justice system helps to reduce public concerns that these programs are not serious, or a place where drug users can avoid prison but can continue to use drugs. The public is more likely to support policies that send offenders to treatment rather than prison if they believe that reliable drug testing is being done and that violators will be sent back to court.

Testing in Schools

There is substantial evidence that young people are increasingly exposed to drugs earlier and earlier in their lives. This exposure often occurs in school settings. As a consequence, there are proposals to perform drug tests of students in schools, including "for cause" testing (also known as suspicion-based testing), random testing of some students, and comprehensive testing of all students. It is believed that drug testing will be a deterrent, or serve to discourage, student drug use. Drug testing of students will also identify drug users early in life and allow treatment while they are still young. The earlier a drug user enters treatment, the more likely the chance of success. School drug-testing programs are geared toward treatment. Students who test positive typically are not criminally prosecuted but are instead referred to drug treatment.

Types of Testing

The term "drug testing" means the use of chemical technology to analyze a biological sample in order to detect the presence of a drug or drug by-product. The most common samples currently used are urine and blood, but hair, sweat, and saliva samples are becoming more popular. The single most frequently used technique for alcohol is breath analysis.

Blood. Drugs can be identified in the blood. However, using blood as a sample can create problems. For example, collecting a blood specimen, or sample, with a hypodermic needle is invasive and painful. There is the possibility of infection from the necessary puncture wound. In addition, blood can be the source of a disease such as AIDS or hepatitis. Blood samples can also be difficult to transport and store (for example, they require refrigeration and the use of special additives or preservatives). Moreover, blood specimens are not very stable and may break down over time and become unusable unless special precautions are taken. Finally, when testing blood, the retrospective period, or the period of time between drug use and the collection of a sample during which a drug can be identified, is quite short for most drugs.

Urine. Urine is the single most frequently used specimen for detecting commonly used illicit drugs. The use of urine samples has many benefits. First, the collection is noninvasive, since urine is collected without any use of needles. Second, urine, unlike blood, is a concentrated fluid, so the amounts of drug materials in the urine are high compared to the levels found in blood. Third, the urine will contain high concentrations of both the drug of interest (often called the parent drug) and drug by-products, or metabolites.

DrugDetection period
Methamphetamine2–3 days
Amphetamine (metabolite of methamphetamine) 
HeroinIn minutes
Morphine (metabolite of heroin)Opiates positive for 2–4 days (EIA)
6-Mono-acetyl-morphine (MAM)Few hours
Phencyclidine (PCP)2–3 days
CocaineFew hours
Benzoylecgonine (metabolite of cocaine)3–5 days
9-Tetrahydrocannabinol90% fall in 1 hour (blood)
9-Tetrahydrocannabinoic acid (marijuana metabolite in urine)Depending on use, few days to many weeks
BenzodiazepinesDays to weeks, depending on half-life
Diazepam2 weeks
Flunitrazepam (rohypnol)0.2% excreted unchanged
Barbiturate (phenobarbital)1–2 weeks after last use
Alcohol (ethanol)1.5–12 hours depending on the peak blood level. Urine typically positive for an additional 1–2 hours.
Gamma-hydroxybutyrate (GHB)Less than 12 hours

The major drawback of using urine samples is that, for many drugs, it has a relatively short retrospective period. For the common drugs of abuse (with the exception of marijuana), urinalysis is unlikely to detect drugs used beyond a past forty-eight-hour "window" of time. This may be longer for marijuana users. Drugs such as cocaine, heroin, ecstasy (MDMA), and other water-soluble drugs, however, have a very small window.

Additional concerns with urinalysis are the possibility of infection from the handling of urine samples, the problems of storage (such as leakage, odor, and so on), and the potential objection that collecting the sample is an invasion of people's privacy. Another weakness of urine specimens is the ease of changing the test outcome by tampering with the sample. A person can secretly place some chemical in the urine, or dilute it with water, to mask the presence of a drug, or even substitute a "clean" sample in place of the person's own urine.

Urine is typically analyzed by a rapid method that relies on immunochemistry or a means of testing that detects the presence of the drug or the drug metabolite. This is usually called a screening method. These tests are very rapid and are done on a large scale by automated equipment. As a result, the cost of doing screenings is quite low. However, in many legal cases, a positive drug screen must be confirmed by a second test that is slower and more expensive.

Hair. The drugs a person consumes become trapped in the user's hair. Laboratory analysis of hair can reveal the presence of a variety of drugs, including heroin, cocaine, amphetamines, phencyclidine, marijuana, nicotine, and barbiturates. Hair analysis is widely accepted by courts, parole boards, and police departments, and has recently been approved by the Food and Drug Administration. Employers around the country are using it for detecting long-term drug use. It is also increasingly used to determine when a pregnant mother has exposed a fetus to drugs and to validate (prove to be true) self-reports of drug use.

See Organizations of Interest at the back of Volume 2 for address, telephone, and URL.

Hair analysis can routinely reveal the use of drugs during the past ninety days (or more, depending on the length of the hair), a much longer period than any other test. Since hair grows at a relatively constant rate of one centimeter per month, analysis of hair strands could pinpoint the time of drug exposure to within as little as one particular week.

Hair analysis has been controversial for a number of reasons. Some see it as more invasive of privacy since hair tests, as compared to other tests, can detect drug use going much farther back before the time of the test. There have also been technical controversies about hair analysis. For example, there is the possibility that various hair treatments, such as tinting and permanents, may remove some of the drugs. However, research has generally shown that detectable traces of drugs do remain in the hair in spite of treatments and vigorous washings.

Another controversial area has been the possibility of hair being contaminated by materials in the environment, rather than through actual, direct use of a drug. This is known as passive contamination. Hair analysis may show exposure to a drug but not necessarily the voluntary use of it. For example, drugs can be deposited on the hair by environmental exposure, such as marijuana smoke or cocaine powder in the air. Furthermore, the materials in the environment may actually be inhaled or swallowed in small amounts. Passive contamination generally can be controlled through careful washing procedures, the use of drug metabolites to indicate true use, and appropriate minimal threshold values for both the parent drug and its metabolites.

Sweat and Saliva. In recent years, both sweat and saliva have been considered as potential samples for drug testing. These materials generally have the same limitations that urine does—a short time frame during which drug presence can be identified. Additionally, saliva, if collected right after drug use, will also be influenced by the amount of possible residual drug in the mouth, so it may not work well as an estimator of blood concentration. Sweat testing has been incorporated into a "sweat patch" that is currently on the market and used as a long-term monitoring device. An absorbent pad with a tamper- proof adhesive is affixed to a person's body (typically the upper arm or upper back). This pad absorbs sweat over a relatively long period of time. If the person has used drugs, the sweat will contain both drugs and drug metabolites, which can be extracted and identified by the same methods referred to above.

Both of these techniques are relatively new and have not yet been widely used, but they may become more prominent in the future. Saliva testing may offer an alternative to urine testing in circumstances that make urine collection difficult or undesirable. Sweat patches may also offer an alternative to hair analysis. However, sweat patches may be subject to the same criticisms as hair testing and may also prove difficult in terms of tampering, removal, or interference with daily routines like washing and participating in sports.

Breath. Breath testing is a technique commonly used by law- enforcement authorities to test for alcohol. Testing can be done with a Breathalyzer or other breath analysis machines. Breath tests actually rely on detecting alcohol in the water vapor that is a component of breath. To determine blood alcohol concentration, the Breathalyzer tests the exhaled breath and the water vapor in it to estimate the blood plasma alcohol concentration. This test is popular because exhaled breath is convenient to collect and is noninvasive, meaning that the skin is not pierced to collect blood or body fluids.

Some devices can preserve the breath sample for later analysis if a Breathalyzer is not immediately at hand. Errors in breath analysis can be caused by the presence of residual alcohol in the mouth. Immediately after drinking, there is enough alcohol vapor in the mouth to give artificially high concentrations when the breath is analyzed. Generally this effect disappears twenty minutes after drinking, but high values for as long as forty-five minutes have been reported.

The Interpretation of Test Results

Problems can occur with the interpretation of drug tests. Two common problems are a false negative and a false positive.

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False Negatives. A false negative occurs when a drug is present but is not identified. The testing method being used may have too high a detection limit—that is, it cannot detect the presence of drugs below a certain level. It is also possible that the absolute quantity of the drug in the specimen is too low. There are several limits imposed on testing instruments. One is the limit of detection, or the lowest concentration the instrument can detect. The second is the threshold or cut-off value, or a value above the limit of detection that is selected based on prior tests. The threshold value is designed to accommodate small amounts of drug that may be present due to passive ingestion or contamination.

Urine tests can yield false negatives if the individual has consumed large amounts of fluids prior to giving the sample. The dilution of the urine "waters down" the final concentration of the drug, reducing it below the threshold value. The result is a false negative.

False negatives can be avoided in several ways. First, in testing for a particular drug, the specimen should be analyzed not only for the drug itself but also for its metabolites. Heroin use, for example, is determined by the presence of its metabolite, morphine. Increasing the amount of specimen for analysis or treating it with chemicals can also make laboratory methods more sensitive.

False Positives. A false positive occurs when a drug is shown to be present but in fact is not. A test can yield a false positive if another drug or substance is present in the specimen that has a reaction to the chemical agents used in analysis. Substances other than the drug being tested for may have a metabolite that will give a positive reaction. For example, at times false positives for amphetamines occur when a person is on allergy medications. Using a second test, one that uses a different technology to confirm the results of the first, can identify false positives.

Cheating on Drug Testing

The most common ways in which subjects of drug screening fool the system are switching "clean" urine for "dirty" urine, submitting urine that is not their own, or saving their own clean urine for later use. Freeze-dried clean urine samples are openly sold for just this purpose.

Other measures include hiding containers of clean urine, trying to substitute other liquids for urine, or adding substances thought to mask the presence of drugs in urine. Because the addition of various substances to urine in an attempt to cover up the presence of drugs is a common practice, many laboratories routinely test for these substances in the urine.

The Ethics of Drug Testing

There is considerable controversy surrounding the ethics of drug testing. Some people oppose drug testing in most or all forms, while others believe it is appropriate to drug-test individuals under most if not all social circumstances. The major points of disagreement between these two groups are over the issues of privacy, impairment, and illegality. Those opposed to drug testing generally see drug use as a private behavior, involving only the person who chooses to take drugs. These people do not believe that drug use causes public harm. Drug testing, they believe, should only be done in response to some measurable harm or evidence of a crime. This group sometimes supports limited drug testing in certain occupations that directly affect public safety, such as airline pilots or police officers.

Those who support widespread drug testing argue that drug use is in itself an activity harmful to society, in addition to being illegal. Therefore, supporters say, the right to privacy is not a compelling argument, since privacy should not be a defense of illegal behavior. In addition, drug users subject others to risk because they cannot use good judgment or fully control their behavior while intoxicated. As a result, supporters argue, the public has a right to be protected from this behavior.

see also Costs of Drug Abuse and Dependence, Economic; Diagnosis of Drug and Alcohol Abuse: An Overview; Driving, Alcohol and Drugs; Schools, Drug Use in; Treatment Types: An Overview; Workplace, Drug Use in the.


  1. ImmunoassaysEnzyme immunoassay (EIA)
    Enzyme-multiplied immunoassay technique (EMIT)
    Fluorescence polarization immunoassay (FPIA)
    Radio immunoassay (RIA)
    Kinetic interaction of microparticles in solution (KIMS)
    Cloned enzyme donor immunoassay (CEDIA)
    Rapid slide tests (point-of-care testing)
  2. Chromatographic MethodsThin-layer chromatography (TLC)
    Liquid chromatography (HPLC)
    Gas chromatography (GC)
  3. Chromatography/Mass SpectrometryGas chromatography/mass spectrometry (GC/MS)
    Liquid chromatography/mass spectrometry (HPLC/MS)