False Negative

Last updated: May 25, 2018

What Does False Negative Mean?

The term false negative is used in urine drug testing to describe a result that indicates a target drug is not present in the sample despite the fact that the test subject has ingested or used the drug. False negatives may occur when a sample has been manipulated by the test subject, or when the testing method fails.

Individuals may intentionally attempt to render a drug test invalid or induce a false negative through various methods. Test subjects may attempt to mask, dilute, or entirely replace a sample in order to avoid detection of the target drug. Many of these methods are well-known in the drug testing industry and specific evaluations have been designed to detect them. However, it is reasonable to assume that not every manipulation will be discovered.


WorkplaceTesting Explains False Negative

The potential for a drug test to result in a false negative is less well-known that its counterpart, the false positive. Yet, the possibility a false negative can be problematic for those tasked with monitoring the status of those who have abused or have the potential to abuse certain drugs. For example, a user of prescription opioids may sometimes be asked to submit to testing to ensure that he or she is not misusing the drug. In such circumstances, a false negative result may prevent caregivers from detecting the of early signs of addiction.

Beyond physical manipulation of a sample, a false negative may occur for reasons related to the individual characteristics of the person being tested, the drugs used, or the screening method employed. Drug tests are usually designed to detect only a specific drug or set of drugs and drug metabolites. Therefore, a test may produce a false negative simply because the analysis of the sample employed the wrong testing panel. For example, a standard toxicology test may detect some, but not all opiates. Alternatively, a drug may be present in a sample but at a concentration that is below the cut-off rate.

Additionally, while the use of cut-offs is intentional and expected, a user with a particularly high metabolic rate may achieve a false negative rate despite having a usage rate that would normally produce a positive result.

In the workplace setting, a false negative puts not only the worker but his or her co-workers and others at risk. Because of this, employers, collectors, and authorized labs should follow appropriate procedures to ensure that false negative results are minimized.


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