A reference test, which added bupropion to drug-free urine, showed that the cross-reactivity of bupropion with the amphetamine immunoassay ranged from 3% to 17%, depending on concentration.¹³ In 53 of these false positives (41%), use of bupropion was documented.¹² A case report also described a patient taking 300 mg of bupropion daily and testing falsely positive for amphetamines. A retrospective chart review of 10,011 urine drug screens found that of 362 initial positive amphetamine tests, 128 (35%) were false positives. In addition to weight-loss supplements, bupropion, which is used as an antidepressant and smoking cessation aid, also is structurally similar to amphetamine and has been associated with false positive screenings. Positive amphetamine screens from 2 initial separate immunoassays were determined to be false positive in confirmatory testing.¹¹ Identifying pseudoephedrine, phenylephrine, and DMAA as possible causes of false positives is especially problematic because they are available over-the-counter, causing some patients to be unaware of their intake. A case report linked a false positive amphetamine screening to use of the weight-loss supplement Oxyelite Pro.¹⁰ In addition, a review of drug screenings conducted by the Department of Defense showed that DMAA was associated in 124 cases out of 134 false-positive amphetamine samples. DMAA has sympathomimetic activity and is an ingredient in some dietary and weight-loss supplements. However, false positives are possible and must be considered when interpreting results.Īnother drug that has been associated with false positive results for amphetamine is 1,3 dimethylamylamine (DMAA). By interacting with specific structures, the immunoglobulins signal the presence of certain drugs.² Immunoassays frequently are used in initial urine drug screenings because they provide rapid results, cost relatively little, and are commercially available. In these tests, a sample of urine or bodily fluid is added to a solution containing antibodies or immunoglobulins, which bind to targeted analytes. Multiple immunoassays are available, and they all share similar basic methodology. Urine screenings for amphetamines commonly involve the use of immunoassays. See strategies for a two-step approach and more specific details on what these tests can and cannot show in our Clinician Guide on Drug Monitoring. Results are expressed as negative or presumptive-positive, and cannot distinguish true-positive from false-positive results.ĭefinitive drug monitoring, which can be more costly, identifies specific drugs and metabolites, and can confirm presumptive results or rule out presumptive false-positives. Presumptive drug monitoring identifies possible use or non-use of drugs or drug classes and includes lab-based immunoassay and point-of-care methods. There are two main types of urine monitoring tests: presumptive and definitive. Urine specimens are typically preferred although oral flued may be used as well. More complex drugs can also show up incorrectly on drug screen results: methadone, opioids, phencyclidine, barbiturates, cannabinoids (see also, a sample case study on marijuana false positives and an ask the expert QA on false-positve marijuana results), as well as benzodiazepines were also reported in patients taking commonly used medications .Īn OTC nasal inhaler can cause a false positive as well. Several common medications can lead to a false positive on a drug screen, including but not limited to: brompheniramine, bupropion, chlorpromazine, clomipramine, dextromethorphan, diphenhydramine, doxylamine, ibuprofen, naproxen, promethazine, quetiapine, quinolones (ofloxacin and gatifloxacin), ranitidine, sertraline, thioridazine, trazodone, venlafaxine, verapamil.Īmphetamine (more on this below) and methamphetamine are the most commonly reported false positive.
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