Levofloxacin, a fluoroquinolone antibiotic, can produce false positives in various drug screening assays. Understanding which assays are most susceptible is key to accurate interpretation of results.
Immunoassays
Levofloxacin’s chemical structure shares similarities with certain drugs, leading to cross-reactivity in immunoassays. This is particularly true for:
- Opioids: Levofloxacin can cause false positives for several opioids, including morphine and codeine, in enzyme-linked immunosorbent assays (ELISA) and other immunoassay formats. Benzodiazepines: Some benzodiazepine immunoassays may also show a false positive in the presence of levofloxacin.
Confirmation testing using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) is crucial to differentiate levofloxacin from these drugs.
Other Assays
While less common, levofloxacin may also interfere with other screening methods. Specific instances are less frequently reported but should still be considered:
Some urine drug screening panels: Depending on the specific panel and the antibody used, false positives might occur. Specific drug classes: The possibility of interference with assays targeting other drug classes cannot be entirely ruled out.
Always consult the assay’s package insert for potential cross-reactivity information, especially if levofloxacin use is suspected.
Recommendations
To minimize false positive results:
- Thorough patient history taking is important for clinical correlation. Consider using confirmatory tests (GC-MS/LC-MS) to verify initial screening results when levofloxacin use is known or suspected. Specify medications on the requisition for drug screens.
Accurate interpretation requires a holistic approach, combining laboratory findings with clinical presentation and patient history.
