From the Guidelines
The most common causes of a false-positive amphetamine test in individuals denying methamphetamine use are prescription medications, such as amphetamine and dextroamphetamine for attention-deficit/hyperactivity disorder, as well as certain foods or substances that metabolize into amphetamine-like compounds. When considering the potential for false-positive results, it is essential to recognize that standard immunoassay screening tests can yield false positives due to cross-reactivity with unrelated substances in the urine, as noted in a study on drug testing in children and adolescents 1. Some key points to consider include:
- Prescription medications like amphetamine and dextroamphetamine can lead to positive test results for amphetamines, which may be misinterpreted as substance abuse.
- Certain foods or substances can metabolize into compounds that are detected by drug tests, leading to false-positive results.
- The limitations of drug testing, including the potential for cross-reactivity and the importance of knowing an individual's complete medical history, must be taken into account when interpreting test results.
- Confirmatory tests, such as gas chromatography-mass spectrometry (GC-MS), can provide more accurate results by identifying the specific substance present, as opposed to standard immunoassay screening tests which have limited specificity. In clinical practice, it is crucial to consider these factors and to request confirmatory testing if an unexpected positive result is obtained, while also disclosing all medications and supplements being taken, as this information can significantly impact the interpretation of drug test results 1.
From the Research
Common Causes of False-Positive Amphetamine Tests
The most common causes of false-positive amphetamine tests in individuals denying methamphetamine use include:
- Cross-reactivity with certain medications, such as:
- Phenylephrine, an α(1)-adrenergic agonist, which can yield a false-positive result for methamphetamine 2
- Imatinib, a medication used to treat chronic myelocytic leukemia, which can lead to false-positive amphetamine results on urine drug testing 3
- Metoprolol, a beta-blocker, which can cause false-positive results for amphetamines and 3,4-methylenedioxymethamphetamine (MDMA) immunoassays 4
- Trazodone, an antidepressant, whose metabolite meta-chlorophenylpiperazine (m-CPP) can cause false-positive urine amphetamine immunoassay results 5
- Other substances that may interfere with urine drug screens, although the provided studies do not specify these substances
Importance of Confirmatory Testing
It is essential to note that immunoassay results should be verified with confirmatory testing, such as gas chromatography-mass spectrometry (GC-MS), to minimize unfavorable consequences 2, 3, 4. This is because immunoassay results may not always be reliable due to cross-reactivity with other compounds.
Clinical Implications
False-positive amphetamine test results can have significant clinical implications, including:
- Incorrect diagnosis and treatment of patients
- Inaccurate assessment of patients for organ donation 2
- Potential legal and social consequences for individuals falsely accused of substance use Therefore, it is crucial to consider the potential for cross-reactivity and to verify immunoassay results with confirmatory testing 2, 3, 4, 5