DRUG TESTING: AN OVERVIEW
One of the most insidious intrusions on Americans’ personal privacy and freedom in recent years has been the increasingly pervasive practice of urine testing. Since the introduction of federal drug testing regulations by the Reagan administration, Americans have more and more often been required to pee in a cup in order to prove their worthiness for employment, insurance, medical treatment, child custody, extracurricular activities in schools, workers’ compensation, security clearance, participation in athletics, military service, and personal liberty from prison. Behind this practice lies the scientifically unwarranted assumption that a person’s fitness can be determined by the chemistry of their urine or other bodily fluids, much like the fictional, crackpot Laputans satirized by Jonathan Swift in Gulliver’s Travels.
In fact, drug testing does not measure fitness or impairment, but rather the presence of certain drug residues that may have no deleterious effect at all. This is especially the case with marijuana, the most popular, safe, and medically useful illegal drug, whose presence is typically detectable for days or weeks after last use by urine testing, long after any impairing effects have faded. Ironically, urine testing is far more sensitive to marijuana than more dangerous drugs, such as opiates, amphetamines, and alcohol (which isn’t even checked for in urine tests). Therefore drug testing can have the counterproductive effect of encouraging workers to move from marijuana to more dangerous, less detectable substances such as designer drugs, alcohol, and prescription narcotics, while at the same time depriving them of the medicinal benefits of cannabis. Moreover, of course, it subjects users and non-users alike to an obnoxious invasion of intimate bodily privacy.
Types of Drug Testing
Urinalysis
By far the most common and abused form of drug testing is urinalysis, in which the subject is required to submit a urine sample for chemical testing. If the test detects more than a certain level of trace marijuana residues, the sample is considered to be “positive” and the subject has failed the test. Most of the information in this booklet refers to urine testing.
It is important to recognize that urine tests do not detect the psychoactive component in marijuana, THC (delta-9-tetrahydrocannabinol), and therefore in no way measure impairment; rather, they detect the non-psychoactive marijuana metabolite THC-COOH, a waste product manufactured by the body which can linger for days and weeks with no impairing effects. Because of THC-COOH’s unusually long elimination time, urinalysis can show a positive result for marijuana for 1–7 days after last use in occasional users, or weeks in regular users. Urine tests are more sensitive to marijuana than most other drugs, which are typically detectable for only a day or two. Labs report that about 50% of all drug test positives are for marijuana.
Blood Tests
Blood tests are a better indicator of recent use because they measure the presence of active THC in the system, which typically lasts hours instead of days. Blood THC spikes dramatically in the first few minutes after smoking, then declines to undetectable levels after a few hours for occasional users. In chronic users, low but detectable levels may persist for up to a week without any impairment because THC is stored in body fat, from which it is slowly released and metabolised.
Because they are invasive and difficult to administer, blood tests are used less frequently. They are typically used in investigations of accidents, injuries and DUIs, where they can give a useful indication of whether the subject has used cannabis recently. In general, high blood THC levels are a likely indicator of being under the influence, while low levels are not correlated with impairment.
Hair Tests
Hair tests are the most objectionable form of drug testing, since they do not measure current use, or even recent use, but rather non-psychoactive residues that remain in the hair for months afterwards. These residues are absorbed internally and do not appear in the hair until 7–10 days after first use.
Hair tests are more likely to detect regular than occasional marijuana use. One study found that 85% of daily users tested positive for marijuana, versus 52% of occasional smokers (1–5 times per week).1 Ingested cannabis was less likely to be detected than smoked marijuana. It is doubtful whether hair tests are sensitive to one-time use of marijuana.
Although hair testing is least useful for detecting on the job use or impairment, that hasn’t stopped employers from using it.
Oral Fluid Testing
Oral fluid testing is a newer, less proven technology that examines saliva samples extracted from the user’s mouth. The tests detect not only marijuana residues that have been left in the mouth by smoking or eating, but also internal residues that are secreted back into the oral tissues from the bloodstream after the drug has been consumed. Oral fluid levels of THC parallel those in blood samples. Depending on the sensitivity of the test, use may be detected for one or two hours up to one to three days, or as long as three weeks in chronic users.
Because oral swabs are less invasive than blood or urine tests, the industry has been eager to adopt the technology. However, reliability problems have so far been an impediment to their widespread adoption. An international study of onsite oral fluid tests concluded than no device was reliable enough to be recommended for roadside screening of drivers.2 While yet to gain official approval from U.S. authorities, oral fluid testing is already approved for use in some foreign countries, such as Australia.
Reliability of Urine Testing
Employment urine screens are by far the most popular and widely used – and abused – type of drug testing. Most U.S. corporations now require urine screens for prospective job applicants and will routinely deny them employment if they test positive for marijuana.
Although urine tests are far from infallible, it is difficult to challenge positive test results. If it comes down to your word versus the lab’s, the lab will almost always win. “False positives,” in which workers are wrongfully accused of a “dirty” sample, are extremely unlikely so long as labs exercise proper procedures. Unfortunately, however, not all labs do so, especially those used by private employers and parties not subject to federal regulation.
In order to prevent false positives, it is essential that every positive urine screen be confirmed by a back-up test and subsequent review by a medical review officer (MRO). The normal procedure is for samples to be initially screened with a so-called immunoassay test (e.g., EMIT, ELISA or RIA), which gives a yes/no result as to whether cannabis has been detected. The test is set to be sensitive to a predetermined cutoff level. The standard cutoff is 50 nanograms per milliliter (ng/ml) of THC-COOH in urine for the Department of Transportation and other federal testing programs (a nanogram equals one billionth of a gram; in different units the limit is 50 micrograms per liter). Because immunoassay screens are vulnerable to urine sample tampering and interference by contaminants, they are not entirely reliable. Also, they don’t give precise results and may register positive above or below their supposed detection threshold.
It is therefore essential that positive samples be confirmed with the more accurate gas chromatograph mass spectrometer (GCMS), which provides an exact, numerical measurement of the amount of THC-COOH in the sample. The GCMS virtually eliminates the chance of false positives in exchange for a relatively high rate of “false negatives,” where levels are below the threshold. To further reduce the possibility of false positives for illicit use, a positive GCMS test still needs to be followed up with an interview by an MRO to determine if there is a legitimate medical reason for the positive test.
The U.S. Substance Abuse and Mental Health Services Administration (SAMHSA) has issued extensive mandatory guidelines for federal workplace drug testing programs.3 SAMHSA guidelines require that positive screens for marijuana be confirmed by GCMS at a level of at least 15 ng/ml, and they require MRO review. The guidelines