In addition to observation and self-reports, biological tests are often used to screen for illicit drug use. These tests include urine, hair, blood, sweat, and oral (saliva) testing.
Urine testing is currently the most common form of drug testing, partly because urine is easy to collect and most drugs can be detected in urine (an exception is methaqualone). Urine testing is good for short term detection, especially of rapidly excreted drugs like cocaine, heroin, and amphetamines, because it is able to provide a view of the past 48 to 72 hours. Urine testing is less effective at detecting long term patterns of drug use.[1-3]
Hair testing is less intrusive and has been used for pre-employment screening. It is also used for investigations when other tests are not available, such as criminal cases or deaths. Hair can be tested for most drugs and has the advantage of providing information over a longer period of time. The life span of a human hair ranges from about four months to four years depending on body location. Drugs enter hair while it is growing and therefore present a record of drug use during the entire period of growth. Hair testing is a better alternative for detecting long term drug use, and it is a process that is more difficult to avoid and tamper with than urine testing. Many drugs are preserved quite stably in hair for months after the administration of the drug. Since hair typically grows 1 cm per month, a 3 cm sample of hair can provide history of drug use for about 90 days. In addition to providing long term use detection, collecting hair samples is less invasive and easier to store than urine.
Some of the disadvantages of hair analysis prevent it from replacing other methods of drug testing. One such disadvantage is that it does not detect short term drug use since drugs are not incorporated in hair immediately. Drugs can only be detected after 3 to 5 days following ingestion since that is the time required for the hair to emerge from the epidermis. Another disadvantage of hair analysis is that the relationship between the drug dosage and levels found in hair has not been clearly established. In addition, some users cut their hair too short or have no head hair making it insufficient to do a hair analysis. However, hair can be collected from other parts of the body like the pubis or axillae (armpits) to provide a hair sample for drug testing. Another issue is that shampoo residues, hair treatments, smoke, air pollution, and other environmental effects may act as contaminates and adversely impact the accuracy of hair testing. Also, dark-haired people have a higher concentration of melanin, which incorporates and retains drugs to a higher degree. The result is that a dark-haired person is substantially more likely to test positive than a lighter-haired person who used the same amount of the drug.
Blood testing is most commonly done for clinical, diagnostic, and drug overdose purposes, and is routine in hospital emergency departments. Blood testing is favored for post-accident investigation because it can be done even with a severely intoxicated, injured, or dead person. Most drugs can be tested in blood, though THC (marijuana) is particularly difficult to measure.
Sweat testing is sometimes used by the criminal justice system to monitor parolees and prisoners. Research has determined that residues of a number of drugs can be detected in human sweat, including alcohol, amphetamine, cocaine, heroin, morphine, methadone, methamphetamine, and phencyclidine (PCP). The process involves wearing a sweat patch, which can be similar to a common band-aid, to collect sweat from participants. The patch, which collects accumulating sweat on an absorbent cellulose pad, is typically designed to be worn for several days, though patches for shorter periods have been developed. To prevent tampering to conceal drug use, the patch is specially designed so that once removed, it cannot be reattached to the skin. The accumulated sweat residue in the patch is assayed by gas chromatography-mass spectrometry, a precise analytical process for separating and identifying chemical compounds. Sweat testing has an advantage in that it is less invasive than urine or blood testing.[3,5,6]
Oral fluid (saliva) testing is conducted by rubbing a swab inside of the cheek, placing it in a sealed container, and then submitting it for testing. Saliva will show amphetamines, barbiturates, cocaine, marijuana, opiates, and PCP. Oral fluid testing is more efficient than urine at detecting recent use but is less effective after three days. Advantages include the ease of collection and the difficulty of adulteration or substitution. This form of testing appears to be growing increasingly popular.[3,7]