False-positives in urine drug screening caused by medications

Testing urine for the presence of drugs has a variety of uses including assessing poisoning or overdose, pre-employment testing, substance abuse treatment monitoring, or other medicolegal purposes.  There are a number of common medications that can cause false-positive screening of these tests which can lead to a variety of ramifications.

Initial tests are usually performed with an immunoassay.  These can generally be done quickly (an hour or two) and inexpensively and vary in their sensitivity.  They may miss particular substances (for opioids in particular – synthetic or semisynthetic opioids such as hydrocodone, oxycodone, fentanyl, or methadone may not test positive on the initial immunoassay) so if you’re suspicious/concerned about a certain agent, let the lab know so the correct test is performed.  Following the immunoassay, positive results can be confirmed with a more specific technique such as gas chromatography or mass spectrometry but these tests are more costly and time consuming so results may not be available for hours to days. 

Here is a table of medications that can cause false-positives on the urine immunoassay and some comments about the caveats of each category.

New drug of abuse comes to America – Enter krokodil

Reports developed in the media last month identifying suspected cases of ‘krokodil’ use in Utah, Arizona, and Illinois.  While the drug’s presence has not officially been confirmed there is a significant health concern when considering this new drug’s properties and what the results of its use are.