via the keratinocytes, the cells responsible for hair growth. these cells form the hair in the root and then grow through the skin surface taking any substances with them. on the other hand, the sebaceous glands produce faees in the scalp and these migrate together with the sebum along the hair shaft (auwärter et al., 2001, pragst et al., 2004). so these glands lubricate not only the part of the hair that is just growing at 0.3 mm per day on the skin surface, but also the more mature hair growth, providing it with a protective layer of fat. faees (nanogram = one billionth of a gram) appear in hair in almost one order of magnitude lower than (the relevant order of magnitude of) etg (picogram = one trillionth of a gram). it has been technically possible to measure faees since 1993, and the first study reporting the detection of etg in hair was done by sachs in 1993. in practice, most hair which is sent for analysis has been cosmetically treated in some way (bleached, permed etc.). it has been proven that faees are not significantly affected by such treatments (hartwig et al., 2003a). faee concentrations in hair from other body sites can be interpreted in a similar fashion as scalp hair (hartwig et al., 2003b). presumptive substance testing presumptive substance tests attempt to identify a suspicious substance, material or surface where traces of drugs are thought to be, instead of testing individuals through biological methods such as urine or hair testing. the test involves mixing the suspicious material with a chemical in order to trigger a color change to indicate if a drug is present. most are now available over-the-counter for consumer use, and do not require a lab to read results. duquenois reagent benefits to this method include that the person who is suspected of drug use does not need to be confronted or aware of testing. only a very small amount of material is needed to obtain results, and can be used to test powder, pills, capsules, crystals, or organic material. there is also the ability to detect illicit material when mixed with other non-illicit materials. the tests are used for general screening purposes, offering a generic result for the presence of a wide range of drugs, including heroin, cocaine, methamphetamine, amphetamine, ecstasy/mdma, methadone, ketamine, pcp, pma, dmt, mdpv, and may detect rapidly evolving synthetic designer drugs. separate tests for marijuana/hashish are also available. there are five primary color-tests reagents used for general screening purposes. the marquis reagent turns into a variety of colors when in the presence of different substances. dille-koppanyi reagent uses two chemical solutions which turns a violet-blue color in the presence of barbiturates. duquenois-levine reagent is a series of chemical solutions that turn to the color of purple when the vegetation of marijuana is added. van urk reagent turns blue-purple when in the presence of lsd. scott test's chemical solution shows up as a faint blue for cocaine base. in recent years, the use of presumptive test kits in the criminal justice system has come under great scrutiny due to the lack to forensic studies, questioned reliability, rendering of false positives with legal substances, and wrongful arrests. saliva drug screen / oral fluid-based drug screen saliva / oral fluid-based drug tests can generally detect use during the previous few days. is better at detecting very recent use of a substance. thc may only be detectable for 2–24 hours in most cases. on site drug tests are allowed per the department of labor. detection in saliva tests begins almost immediately upon use of the following substances, and lasts for approximately the following times: alcohol: 6-12 h marijuana: 1-24h a disadvantage of saliva based drug testing is that it is not approved by fda or samhsa for use with dot / federal mandated drug testing. oral fluid is not considered a bio-hazard unless there is visible blood; however, it should be treated with care. sweat drug screen sweat patches are attached to the skin to collect sweat over a long period of time (up to 14 days). these are used by child protective services, parole departments, and other government institutions concerned with drug use over long periods, when urine testing is not practical. there are also surface drug tests that test for the metabolite of parent drug groups in the residue of drugs left in sweat. an example of a rapid, non-invasive, sweat-based drug test is fingerprint drug screening. this 10 minute fingerprint test is in use by a variety of organisations in the uk and beyond, including within workplaces, drug treatment and family safeguarding services at airport border control (to detect drug mules) and in mortuaries to assist in investigations into cause of death. blood drug-testing a blood sample measures whether or not a drug or a metabolite is in the body at a particular time. these types of tests are considered to be the most accurate way of telling if a person is intoxicated. blood drug tests are not used very often because they need specialized equipment and medically trained administrators. depending on how much marijuana was consumed, it can usually be detected in blood tests within six hours of consumption. after six hours has passed, the concentration of marijuana in the blood decreases significantly. it generally disappears completely within 30 days. random drug testing can occur at any time, usually when the investigator has reason to believe that a substance is possibly being used by the subject by behavior or immediately after an employee-related incident occurs during work hours. testing protocol typically conforms to the national medical standard, candidates are given up to 120 minutes to reasonably produce a urine sample from the time of commencement (in some instances this time frame may be extended at the examiners discretion). diagnostic screening in the case of life-threatening symptoms, unconsciousness, or bizarre behavior in an emergency situation, screening for common drugs and toxins may help find the cause, called a toxicology test or tox screen to denote the broader area of possible substances beyond just self-administered drugs. these tests can also be done post-mortem during an autopsy in cases where a death was not expected. the test is usually done within 96 hours (4 days) after the desire for the test is realized. both a urine sample and a blood sample may be tested. a blood sample is routinely used to detect ethanol/methanol and asa/paracetamol intoxication. various panels are used for screening urine samples for common substances, e.g. triage 8 that detects amphetamines, benzodiazepines, cocaine, methadone, opiates, cannabis, barbiturates and tricyclic antidepressants. results are given in 10–15 min. similar screenings may be used to evaluate the possible use of date rape drugs. this is usually done on a urine sample. optional harm reduction scheme drug checks/tests (also known as pill testing) are provided at some events such as concerts and music festivals. attendees can voluntarily hand over a sample of any drug or drugs in their possession to be tested to check what the drug is and its purity. the scheme is used as a harm reduction technique so people are more aware of what they are taking and the potential risks. occupational harm reduction strategies drug and alcohol impairment while at work increases the risk of work-place accidents and decreases productivity. employers such as the commercial driving and airline industry may conduct random drug tests on employees with the goal of deterring use to improve safety. there is some evidence that increasing the use of random drug testing in the airline industry reduces the percentage of people who test positive, however, it is unclear if this decrease is associated with a corresponding decrease in fatal or non-fatal injuries, other accidents, number of days absent from work. it is also not clear if there are other unwanted side effects that may result from random drug and alcohol testing in the workplace. commonly tested substances anabolic steroids anabolic steroids are used to enhance performance in sports and as they are prohibited in most high-level competitions drug testing is used extensively in order to enforce this prohibition. this is particularly so in individual (rather than team) sports such as athletics and cycling. methodologies before testing samples, the tamper-evident seal is checked for integrity. if it appears to have been tampered with or damaged, the laboratory rejects the sample and does not test it. next, the sample must be made testable. urine and oral fluid can be used "as is" for some tests, but other tests require the drugs to be extracted from urine. strands of hair, patches, and blood must be prepared before testing. hair is washed in order to eliminate second-hand sources of drugs on the surface of the hair, then the keratin is broken down using enzymes. blood plasma may need to be separated by centrifuge from blood cells prior to testing. sweat patches are opened and the sweat collection component is removed and soaked in a solvent to dissolve any drugs present. laboratory-based drug testing is done in two steps. the first step is the screening test, which is an immunoassay based test applied to all samples. the second step, known as the confirmation test, is usually undertaken by a laboratory using highly specific chromatographic techniques and only applied to samples that test positive during the screening test. screening tests are usually done by immunoassay (emit, elisa, and ria are the most common). a "dipstick" drug testing method which could provide screening test capabilities to field investigators has been developed at the university of illinois. after a suspected positive sample is detected during screening, the sample is tested using a confirmation test. samples that are negative on the screening test are discarded and reported as negative. the confirmation test in most laboratories (and all samhsa certified labs) is performed using mass spectrometry, and is precise but expensive. false positive samples from the screening test will almost always be negative on the confirmation test. samples testing positive during both screening and confirmation tests are reported as positive to the entity that ordered the test. most laboratories save positive samples for some period of months or years in the event of a disputed result or lawsuit. for workplace drug testing, a positive result is generally not confirmed without a review by a medical review officer who will normally interview the subject of the drug test. urine drug testing urine drug test kits are available as on-site tests, or laboratory analysis. urinalysis is the most common test type and used by federally mandated drug testing programs and is considered the gold standard of drug testing. urine based tests have been upheld in most courts for more than 30 years. however, urinalysis conducted by the department of defense has been challenged for reliability of testing the metabolite of cocaine. there are two associated metabolites of cocaine, benzoylecgonine (bz) and ecgonine methyl ester (eme), the first (bz) is created by the presence of cocaine in an aqueous solution with a ph greater than 7.0, while the second (eme) results from the actual human metabolic process. the presence of eme confirms actual ingestion of cocaine by a human being, while the presence of bz is indicative only. bz without eme is evidence of sample contamination, however, the us department of defense has chosen not to test for eme in its urinalysis program. a number of different analyses (defined as the unknown substance being tested for) are available on urine drug screens. spray drug testing spray (sweat) drug test kits are non-invasive. it is a simple process to collect the required specimen, no bathroom is needed, no laboratory is required for analysis, and the tests themselves are difficult to manipulate and relatively tamper-resistant. the detection window is long and can detect recent drug use within several hours. there are also some disadvantages to spray or sweat testing. there is not much variety in these drug tests, only a limited number of drugs can be detected, prices tend to be higher, and inconclusive results can be produced by variations in sweat production rates in donors. they also have a relatively long specimen collection period and are more vulnerable to contamination than other common forms of testing. hair drug testing hair drug testing is a method that can detect