The nation's rush to screen workers for evidence of drug use rests on the premise that drug tests yield consistently reliable results. But such tests in fact are fraught with limitations and can cause people to be falsely labeled as drug users, experts in the field say.
The most popular screening tests can mistake ordinary over-the-counter medications like Midol, Dristan or Triaminic-DM for illegal drugs. Such tests also can be easily fooled by drug users who dilute their urine sample. In addition, the tests are incapable of detecting certain substances, such as "designer" drugs.
Moreover, experts agree, faulty laboratory equipment or procedures, as well as sloppy work by ill-trained technicians, can easily lead to erroneous test results.
Errors also can occur because some types of tests require subjective interpretations, turning on questions such as the location, size and color of spots on a piece of laboratory plastic.
Finally, both critics and proponents agree, the tests are incapable of measuring actual impairment at the time a urine sample was given. The tests merely signal the presence of a drug, not the effect it is having on the user. In some cases, the traces of a drug consumed days earlier will still register on a test. Cocaine and heroin, for example, can be detected for as many as two days after use and marijuana for a month or more--long after any effects have worn off.
"There are some very real problems here with what is being asked of these tests and what they can deliver," said UCLA psycho-pharmacologist Ronald Siegel. "The widespread testing and reliance on telltale traces of drugs in the urine is simply a panic reaction invoked because the normal techniques (of controlling drug use) haven't worked very well. The next epidemic will be testing abuse."
Added William H. Anderson, a physician at the Harvard Medical School: "The misuse of screening tests generally seems to arise not out of malice or insensitivity, but rather because of genuine lack of understanding of the limitations of this technology."
Many of the problems that can cause unreliable test results, however, can be overcome.
For example, experts say, any urine sample that leads to a positive result should be tested a second time for confirmation--preferably using a different kind of test, to minimize the likelihood of a false reading.
And to avoid a simple mix-up of urine samples, experts further recommend a rigorous "chain of custody" procedure that closely tracks a specimen from the time it is produced through the completion of the analytical process.
Most companies now are requiring confirmation of initial positive results. But some state prison systems are not, or else are not confirming positive results by accepted techniques.
"Would you want your physician making the decision to operate on you on the basis of a single blood or urine test? No. You would want other tests, a second opinion, and so forth," Siegel said. "But in the workplace, a lot of workers are being 'operated on'--severed from their jobs, prevented from getting jobs, etc., on the basis of a single chemical test."
Added Anderson, a medical epidemiologist: "The rule of thumb has to be: Never do anybody harm on the basis of a single test."
Corrections Being Made
To be sure, some employers are belatedly recognizing the limitations of the existing drug screening tests and are making mid-course corrections in their testing programs. Some such changes are being made only as a result of lawsuits or court verdicts.
In February, for instance, U.S. District Judge Louis F. Oberdorfer ordered the reinstatement of a District of Columbia school bus attendant who was fired after a single positive test for marijuana during an annual physical. He ruled that an employee who tests positive cannot be fired without a second, confirmatory test, citing instructions of the test's manufacturer that any positive finding should be confirmed by an alternate test.
"A few years ago, when some companies did use unconfirmed tests to discharge employees, there was a serious problem," according to Robert L. DuPont, president of the Center for Behavioral Medicine in Rockville, Md., and former head of the National Institute on Drug Abuse.
"Today, virtually all . . . positive tests are confirmed using a different method of analysis," DuPont said. "The possibility of some non-drug substance causing a false positive under such circumstances is virtually zero."
Because of the inherent limitations of most urine tests, many experts say, such a standard also should be extended to job applicants as well as people already on the payroll.
Drug use screening got its start in the mid-1960s amid concerns that American soldiers were becoming addicted to heroin and other drugs in Vietnam.
At the time, the only available technique for urine screening was thin-layer chromatography, commonly referred to as TLC. (Please see accompanying graphic.)