Urine drug screenings are useful diagnostic tests. In chronic pain management, drug testing can assess the appropriate intake of drugs, help with the diagnosis of substance abuse, and improve drug management. Screening for illicit drugs, including amphetamine, can be useful in assessing and monitoring patients with chronic pain. It is important to consider the potential for false positive results when the results of urine drug screenings for amphetamines are interpreted.
Urine screenings for amphetamines commonly involve the use of immunoassays. Multiple immunoassays are available, and they all share similar basic methodology. In these tests, a sample of urine or bodily fluid is added to a solution containing antibodies or immunoglobulins, which bind to targeted analytes. By interacting with specific structures, the immunoglobulins signal the presence of certain drugs. Immunoassays frequently are used in initial urine drug screenings because they provide rapid results, cost relatively little, and are commercially available. However, false positives are possible and must be considered when interpreting results.
Positive amphetamine immunoassay screening test results can be 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 can be linked to a single molecular compound, GC-MS is much more specific than immunoassays and can detect the presence and amount of each drug screened.
While urine drug screenings are valuable tools in pain management, they have limitations, including the potential for false positives. For amphetamines, most incidents of false positives can be related to a drug’s structure, but case reports and retrospective reviews have associated many drugs with false 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 recent medications should be conducted, with additional analysis with more specific tests such as GC-MS, if warranted.