What can cause a false positive result for cocaine in a drug test?

Causes of False Positive Cocaine Test Results

Several substances can cause false positive results for cocaine in drug tests, including medications such as pseudoephedrine, dextromethorphan, and certain antihistamines, as well as some foods containing poppy seeds. 1

Common Causes of False Positive Cocaine Results

Medications

• Over-the-counter medications:
  • Pseudoephedrine (decongestant)
  • Dextromethorphan (cough suppressant)
  • Certain antihistamines
  • Some antidepressants 1

Medical Procedures

• Medicinal cocaine use:
  • Cocaine used as a topical anesthetic in ENT procedures and nasal surgeries can cause positive test results for up to 72 hours 2
  • Important to note that this is a true positive (not false), but may be from legitimate medical use rather than illicit use

Food Products

• Poppy seeds can cause false-positive results 3

Sample Issues

• Adulterated samples can affect test results 3
• Substituted samples (someone else's urine) 3
  • Healthcare providers should check if sample is at body temperature
  • For pregnant women, samples can be tested for human chorionic gonadotropin to verify authenticity

Testing Limitations

• Immunoassay-based tests are susceptible to cross-reactions causing false positives 1
• Improper sample size in field tests can lead to false results 4
• Timing of testing is critical - testing after medication administration can lead to confusing results 3

Avoiding Misinterpretation

Best Practices

1. Document all current medications the patient is taking before interpreting results 1
2. Use confirmatory testing with gas chromatography/mass spectrometry (GC-MS) or liquid chromatography/mass spectrometry (LC-MS/MS) for definitive results 1
3. Consider timing of tests - women should be tested before receiving any medications that could cause positive results, especially in labor and delivery settings 3
4. Discuss unexpected results with patients in a non-judgmental manner before taking action 1

Special Considerations

• In cases of suspected cocaine-induced vasculitis versus granulomatosis with polyangiitis (GPA), specialized testing may be needed as both can present with positive c-ANCA and PR-3 3
• Illicit cocaine may contain additives like levamisole that can cause additional clinical manifestations 3

Clinical Implications

• False positives can have serious consequences for patients, including inappropriate treatment decisions or legal ramifications
• Understanding the limitations of drug testing is essential for proper interpretation
• When a positive result occurs, confirmatory testing should be performed before making clinical decisions 1
• Unexpected positive results should prompt a conversation with the patient rather than immediate punitive action 1

Drug testing interpretation requires knowledge of potential cross-reactants, proper testing methodology, and appropriate confirmation techniques to avoid misdiagnosis and inappropriate patient management.