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Addiction and Substance Abuse

Cause of false positive drug screen

12/18/2006

Question:

A friend of mine passed in an accident. The postmortem toxicology report showed an elevated alcochol level as well as less than 149ng benzoylecgonine, a metabolite of cocaine. This person never exhibited any signs of addiction. She had a scripts for oxycodone, prozac,nirvam. She also had cold symptoms and could have taken a over the counter medication. No traces of opiates were listed on coronor`s report. I assume the test done was a blood test. Could this have been a false positve and what might be the cause if so. The blood test would have been performed appoximately 9-10 hrs after estimated time of death. The death was caused due to traumatic injury from an mva.

Answer:

Thank you for your question. I am very sorry for your loss. To the best of my knowledge, benzoylecgonine is an extremely accurate test for cocaine and no other prescription medication, over-the-counter medication, or other substance except for cocaine will cause benzoylecgonine to appear in blood or urine.

I have read of cases where someone drank South American herbal tea that contained coca leaf extracts and tested positive for benzoylecgonine--however, this is because cocaine comes directly from the leaves of the coca plant. I also know that in some cases, a blend of cocaine and other medications is used to stop very severe nosebleeds in emerg

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Response by:

Christina M Delos Reyes, MD Christina M Delos Reyes, MD
Assistant Professor of Psychiatry
School of Medicine
Case Western Reserve University