The Laboratory's Role in Opioid Pain Medication Monitoring

Opioid analgesics are the most potent pain medications therefore they are often used for the treatment of chronic malignant and non-malignant pain. Their strong addictive potential requires close monitoring of patients on opioid therapy for possible non-compliance with prescriptions, for drug diversion, and for proof of avoidance of non-prescribed or illicit opioids. Monitoring can be performed by urine drug screens or qualitative or quantitative drug confirmation assays. Natural, semi-synthetic and synthetic opioids have dissimilar chemical structures and they undergo extensive metabolism. Phase one metabolic reactions of opioids can produce other opioids with similar structures to other, non-prescribed medications. Only detailed and concurrent analysis of parent drugs and metabolites can provide accurate clinical information regarding patient compliance. Traditional immunoassays, often used for urine drug screening, react with only a small number of opioids or only with a single medication and they exhibit variable cross reactivity with their phase two metabolites. Additionally the limit of detection of these immunoassays may not be sufficient for medical purposes, therefore clinical interpretation of immunoassay test results can be challenging. Recently liquid chromatography, mass spectrometry (LCMSMS) based assays have been adapted by many clinical laboratories. These LCMSMS tests can provide information about the presence of several opioids and their metabolites in a single sample at clinically meaningful detection limits, allowing accurate assessment of patient compliance. This review article will investigate in details the various opioids, their metabolism and the challenges the testing laboratories and ordering clinicians face.