Academy of Diagnostics & Laboratory Medicine - Scientific Short
Scientific Shorts are brought to you by the
For patients with substance use disorders, urine drug testing has an important role in optimizing opioid agonist therapy, assessing compliance and supporting harm reduction efforts by providing information on exposures and associated risks. It is therefore essential that the laboratory has the capability to detect drugs that can be life-threatening, either on their own or in combination with other compounds including novel psychoactive substances (NPS). The increasing diversity of NPS in recent years has made their detection challenging for laboratories, a difficulty compounded by their dramatically expanding availability.
For laboratories that perform an immunoassay screen followed by a mass spectrometry confirmation, retrospective analyses can be utilized to identify the presence of NPS.
In our laboratory, we identified a significant discrepancy between our immunoassay results and mass spectrometry confirmation for benzodiazepines, with the immunoassay results being positive and mass spectrometry results being negative. The discrepancy was so large (49%), that it was outside of what could reasonably be attributed to false positive immunoassay results due to the presence of interferences or cross reactivity. As our mass spectrometry confirmation method is targeted, we investigated the possibility that NPS benzodiazepines were missing from our confirmation panel.
The prevalence of benzo-dope, a mixture of benzodiazepines and opioids has increased significantly over the past couple of years. This combination can be dangerous as it increases the risk of respiratory depression and death1. Benzo-dope preparations are known to include benzodiazepine NPS.
Monitoring drug seizure records and reports detailing emerging substances helped guide which NPS compounds to add to our mass spectrometry confirmation panel. Using this information, we added the following analytes: bromazolam, flualprazolam, flubromazolam and flubromazepam and their metabolites. We then re-tested samples that screened positive for benzodiazepines but confirmed negative, over a period of 6-months.
Adding these NPS benzodiazepines to our confirmation panel significantly increased the agreement between screening and confirmation results for benzodiazepine positives, from 0% to 95.8%. The discrepancies observed between immunoassay screen and confirmation were due to the presence of NPS benzodiazepines commonly found in benzo-dope preparations, which were not included in our mass spectrometry confirmation panel.
When NPS are structurally similar to target analytes, the cross-reactivities of immunoassays can be exploited to identify the presence of NPS. Retrospective data analysis comparing immunoassay with mass spectrometry results can be useful in monitoring false positive rates, as an increase in these rates may indicate the presence of an NPS compound.
