Causes for Failed Drug Tests

Frustrated by what they consider a lack of personal accountability, employers are increasingly relying on drug testing to keep their workforce honest. However, as critics of the practice note, drug testing is not infallible. Failure to follow procedures can yield inconclusive or falsely positive results for illegal drugs, including opiates like heroin or cocaine. Although poppy seeds have been discredited in this regard, the list of substances that can create skewed results is a lengthy and surprising one.

Types

• Not all drug tests are created equal. For example, as the authors of www.drugdetection.net point out, a urine test only shows if someone recently used an illegal drug, but not for how long, nor the type of substance involved. Blood tests are considered most accurate. However, their cost makes employers less likely to use them, according to the site, www.erowid.org. Sweat testing---which requires wearing a patch for extended periods---is the most controversial method, because of surface contamination that may cause false readings.

Significance

• Failing to strictly follow procedures can lead to skewed results. According to drugdetection.net, digital thermometers should be used to certify urine test results within a 96 to 99 degree temperature range. Current practice by the U.S. Substance Abuse and Mental Health Administration allows a 90 to 100 degree range, opening the door to a wide range of inaccurate results. For similar reasons, testing strips that are attached to vials should also not be used, to avoid compromising the sample.

Considerations

• Adhering to the limit of detection is an important principle of proper testing, drugdetection.net states. This means that a specified amount can be present, yet still reported as negative, decreasing the chances of false negatives---or results that may be interpreted as negative, when the drug is present. Random notification is equally critical, since the body has various timetables for clearing itself of a particular drug, drugdetection.net reports. A 24-hour limit is considered the most acceptable.

Over-The-Counter Medications

• Many commonly used drugs can lead to false positive results.

  Taking prescription or over-the-counter medications can skew drug tests. More than 300 examples of drugs exist in both categories, www.erowid.org advises, including cold pills, diet medications, and even hay fever remedies. Also on the list are most over-the-counter nasal decongestants, which have been linked to amphetamine readings, and cold relievers that contain codeine---which may show up as opiate abuse, the site advises. Certain dental products, like Novocaine, have also been known to cause false positive positive readings for cocaine abuse, as well.

Secondhand Exposure

• Worries about false positive results do not stop with the body. Exposure to smoke from crack cocaine, or marijuana---which might be present at concerts, or parties---can be absorbed into the hair, according to information posted on www.Collegebound.com. Sufficient exposure to secondhand smoke from the two substances can also cause the failure of standard drug urine tests, as well. This can lead to failure of a primary and secondary drug test, "with no recourse other than saying that it was someone else," the site advises.