Clinical implications of opioid parent-metabolite ratios

The opioid epidemic has underscored the importance of urine drug testing in the management of chronic pain. However, interpreting test results can be challenging, especially in scenarios where medications may have been directly added to urine samples to simulate compliance.

We conducted a retrospective analysis of 9,690 opioid testing results using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The study aimed to define the expected ratios between parent drugs and metabolites for eight commonly prescribed opioids. Cases with a parent-metabolite ratio above the 95th percentile were subjected to chart review.

A total of 13 cases appeared likely consistent with simulated compliance with buprenorphine, 2 with methadone, 14 with oxycodone, and one with hydrocodone. The unusual patterns of parent-metabolite ratio can also be associated with hyperacute drug exposures/use, pharmaceutical impurity, or underlying liver enzyme deficiency. Furthermore, patients who failed the decision limits could exhibit other illicit use or aberrant behaviors.

Laboratories conducting LC-MS/MS-based opioid testing can more objectively identify anomalies by analyzing parent-metabolite ratios. When in consultation with providers, laboratories can point to these data when suggesting the possibility of simulated compliance and help identify cases warranting further investigation.