What Can Show a False Positive for Methamphetamine
January/February 2015
Drug Monitoring and False Positives
Urine drug screenings are useful diagnostic tests. In chronic pain direction, drug testing can assess the appropriate intake of drugs, help with the diagnosis of substance corruption, and amend drug management.1Screening for illicit drugs or misused medications tin can be useful in assessing and monitoring patients with chronic pain. It is important to consider the potential for fake positive results (ie, incorrect indications) when the results of urine drug screenings are interpreted. Note that false negatives can besides occur, when a drug is present in the patient's organisation merely not showing upwardly on the screening results.
Drugs That Tin Cause False Positives
Several mutual medications can lead to a simulated positive on a drug screen, including but non express to: brompheniramine, bupropion, chlorpromazine, clomipramine, dextromethorphan, diphenhydramine, doxylamine, ibuprofen, naproxen, promethazine, quetiapine, quinolones (ofloxacin and gatifloxacin), ranitidine, sertraline, thioridazine, trazodone, venlafaxine, verapamil.
Amphetamine (more on this below) and methamphetamine are the most commonly reported false positive. More complex drugs tin also show up incorrectly on drug screen results: methadone, opioids, phencyclidine, barbiturates, cannabinoids (see also, a sample instance study on marijuana simulated positives and an enquire the expert QA on simulated-positve marijuana results), every bit well as benzodiazepines were also reported in patients taking commonly used medications .
An OTC nasal inhaler can cause a imitation positive as well.
How Drug Tests Are Washed
Urine specimens are typically preferred although oral flued may exist used also. There are two main types of urine monitoring tests: presumptive and definitive.
Presumptive drug monitoring identifies possible use or not-utilize of drugs or drug classes and includes lab-based immunoassay and indicate-of-care methods. Results are expressed as negative or presumptive-positive, and cannot distinguish true-positive from false-positive results.
Definitive drug monitoring, which can exist more than plush, identifies specific drugs and metabolites, and tin can confirm presumptive results or rule out presumptive false-positives. 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.
Imitation Positive for Amphetamines
Urine screenings for amphetamines ordinarily involve the apply of immunoassays. Multiple immunoassays are available, and they all share like bones methodology. In these tests, a sample of urine or actual fluid is added to a solution containing antibodies or immunoglobulins, which bind to targeted analytes. By interacting with specific structures, the immunoglobulins bespeak the presence of sure drugs.2 Immunoassays frequently are used in initial urine drug screenings because they provide rapid results, cost relatively little, and are commercially available. However, fake positives are possible and must be considered when interpreting results.
Immunoassays often lack the specificity to target private drugs and typically screen for structurally related compounds. Immunoassays for amphetamines can discover several related chemicals, including methamphetamine, 3,iv-methylenedioxyamphetamine (MDA), three,4-methylenedioxymethamphetamine (MDMA), and methylenedioxyethylamphetamine (MDEA), that share a common structure that includes a phenyl ring and an amino group connected by a ii-carbon side chain.3 Withal, these structural elements also tin be found in other non-amphetamine drugs as shown in Figure 1 (beneath), and this may effect in faux positive urine screenings.4-7
For example, the ordinarily used decongestants pseudoephedrine and phenylephrine share similar structural characteristics with amphetamines, and cross-reactivity with screenings has been documented.2,eight A example report linked the use of intravenous (Iv) phenylephrine to a false positive amphetamine screening.9 Upon admission, the patient's routine immunoassay for amphetamines showed a negative result, but subsequently three days, a repeat analysis was positive for amphetamine. A confirmatory test was ordered and identified IV phenylephrine every bit a probable cause of the imitation positive.
Another drug that has been associated with simulated positive results for amphetamine is 1,3 dimethylamylamine (DMAA). DMAA has sympathomimetic action and is an ingredient in some dietary and weight-loss supplements. A case written report linked a faux positive amphetamine screening to use of the weight-loss supplement Oxyelite Pro.10 In add-on, a review of drug screenings conducted by the Section of Defense showed that DMAA was associated in 124 cases out of 134 fake-positive amphetamine samples. Positive amphetamine screens from 2 initial divide immunoassays were adamant to be false positive in confirmatory testing.11 Identifying pseudoephedrine, phenylephrine, and DMAA as possible causes of fake positives is peculiarly problematic considering they are bachelor over-the-counter, causing some patients to be unaware of their intake.
In addition to weight-loss supplements, bupropion, which is used as an antidepressant and smoking abeyance help, also is structurally similar to amphetamine and has been associated with faux positive screenings. A retrospective nautical chart review of 10,011 urine drug screens establish that of 362 initial positive amphetamine tests, 128 (35%) were imitation positives. In 53 of these false positives (41%), utilize of bupropion was documented.12 A case study besides described a patient taking 300 mg of bupropion daily and testing falsely positive for amphetamines. 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
Other drugs can undergo metabolism and crusade false positive results. Meta-chlorophenylpiperazine, a metabolite of trazodone, has shown in vitro activeness with a Roche amphetamine urine immunoassay. Testing of 6 patients taking trazodone showed that 3 tested falsely positive for amphetamines.14 Labetalol, promethazine, chlorpromazine, and metformin also accept been associated with faux positive amphetamine screenings.xv-17 Fenofibrate was identified as the cause of a fake positive urine amphetamine screening in a patient after ii dissever immunoassays were positive.17 In that case, fenofibrate was discontinued, after which repeat urine screenings were negative.
Follow-up Drug Testing and Amphetamines
Positive amphetamine immunoassay screening test results tin exist confirmed with gas chromatography-mass spectrometry tests (GC-MS). GC-MS separates samples into fragments that are specific to each individual compound. Because each fragment pattern tin exist linked to a unmarried molecular compound, GC-MS is much more specific than immunoassays and tin detect the presence and amount of each drug screened.18
While urine drug screenings are valuable tools in hurting management, they have limitations, including the potential for false positives. For amphetamines, well-nigh incidents of simulated positives tin can exist related to a drug's construction, but case reports and retrospective reviews accept associated many drugs with faux positives. Following a positive drug screening, the possibility of a false positive always should be considered. A thorough review of the patient's vital signs, relevant history, and contempo medications should be conducted, with additional analysis with more than specific tests such equally GC-MS, if warranted.
Last updated on: September seven, 2021
Ask The Expert: Simulated-Positive Screen for Benzodiazepines
Source: https://www.practicalpainmanagement.com/resources/diagnostic-tests/ask-expert-false-positive-amphetamine-urine-screens
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