The rise in the use of opioids for pain management and illicit use has increased the need for urine drug testing laboratories to monitor a wide range of opioid analytes. Detection and confirmation of drug analytes in urine is typically done with a preliminary immunoassay and subsequent analysis using GC/MS or LC/MS. Liquid chromatography coupled with quadrupole mass spectrometers and high resolution accurate mass (HRAM) instrumentation is becoming more prevalent for confirmation of drug analytes due to its improved specificity, shorter run times, simpler sample preparation, and lower detection limits. However, laboratories must be aware that this instrumentation may not be able to separate interferences arising from isomeric metabolites that are not typically monitored. The use of a non-selective β-glucuronidase may increase the detection levels of these metabolites. The presence of these interferences was discovered during the development of a 47-analyte HRAM LC-MS/MS UDT method and these interferences are reported here.
75 μL of patient urine sample was combined with 300 μL of master mix containing internal standards and IMCSzyme®. The presence of isomeric metabolites not typically monitored in patient urine samples is something urine drug testing labs must be aware of to avoid over-reporting or obtaining false positives. Because these metabolites are present only in patient samples, external controls are not a good indicator that a method is free of interference.
Information summarized from the technical presentation ” Isomer interferences observed during the development of a 47-analyte HRAM LC-MS/MS method for urine drug testing” presented by Dominion Diagnostics at MSACL 2017