Understanding How a False Positive Urine Test Can Occur

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What is a False Positive Urine Test?

If you have taken a urine test that has tested positive for a particular substance(s) that you have not come in contact with via ingestion, inhalation or injection, the result is considered a false positive, in reference to toxicology. Whether drug testing is required for an employer, school or any other reason, there are a few common causes of false positive urine results and some may be avoidable. However, these findings are not limited to drugs. Screenings for certain enzymes, bacteria and other substances pertinent for diagnostic purposes may also render a false result.

Drug Testing and Medications

A positive toxicology result may be caused by certain medications, including both over the counter and prescription drugs. This can include antihistamines and decongestants containing pseudoephedrine, medications for narcolepsy and ADHD, such as dextroamphetamine, naproxen, an anti-inflammatory drug for conditions such as arthritis and Vick’s inhalers. In addition to this, weight loss supplements can alter toxicology screenings. Those that have recently undergone surgery can obtain a false positive reading as the result of medications administered while in the hospital. Even Amoxicillin has the potential to alter urine testing for drugs.

What About Urine Testing for Diagnostic Purposes?

It is possible to obtain false results with these types of tests as well. Although medications can play a significant role in this, it can depend on the particular type of test. One of the most common causes of a false positive result is failure to properly prepare for the urine test. This can include not fasting prior to the test, utilization of herbal supplements and even strenuous exercise. Once again, these factors are often dependent on what the particular urinalysis is for. Contamination of the specimen is also another consideration when it comes to urine tests. This can occur when the proper procedure for handling and storage is not followed. Not only does this apply to false positive results, but to false negative results as well.

Other Considerations When Dealing With a False Positive Urine Test

False urinalysis tests are not that common, but can occur. In most cases, follow up testing or confirmatory testing is performed following a positive result. This applies to both toxicology and diagnostic testing. One of the easiest ways to prevent a false result is by alerting your physician to any medications you may be taking, prescription or over the counter, and usage of herbal remedies. Always ensure that you understand orders regarding fasting and medications prior to your test day. If you have any concerns about the test and obtaining an inaccurate result, discuss this with your physician prior to testing.


Addiction and Substance Abuse. NetWellness. www.netwellness.uc.edu Reviewed 12, May 2010. Viewed 21, October 2010. https://www.netwellness.uc.edu/healthtopics/substanceabuse/drugtesting.cfm

The Abnormal Urinalysis. Pediatric Clinics of North America. Viewed 21, October 2010. https://www.medicine.nevada.edu/residency/lasvegas/pediatrics/documents/AbnormalUrinalysis_000.pdf