Naloxone (Narcan) is an opioid antagonist that may cause a false-positive immunoassay for opiates. Naloxone may be administered to a patient who presents with stupor or coma to the Emergency Department.
Clinical findings::
(1) positive immunoassay for opioids
(2) history of naloxone administration prior to collection of the specimen used for drug testing
(3) variable evidence for prior opioid exposure
(4) failure of confirmatory testing to detect an opiate, or detection of an opiate at a level lower than suspected from the positive immunoassay
(5) presence of naloxone on confirmatory testing (which often is not done unless specifically ordered)
The presence of a false-positive immunoassay would go unnoticed if the patient had been exposed to opiates prior to naloxone administration. A discrepancy might only be noticed if there was no chance of prior opiate exposure or if the confirmatory testing is negative for opiates or if testing for naloxone is performed.
This risk highlights the need to:
(1) to test samples collected prior to drug administration
(2) to accurately record the times that all drugs are given and all samples are collected
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