Use of Metabolic Ratios of Drugs in Urine for Monitoring Pain Management Patients

Abstract

This is my opinion about the utility of urine metabolic ratios (MRs)2 in the setting of providing laboratory services for pain management patients. In the following sections, I define the MR and some terms related to it, and describe the urine drug testing services at my institution. The MR's utility and limitations are then reviewed, followed by a summary. This institution's core/chemistry laboratory serves the immediate drug testing needs of the 950-bed main hospital, its emergency department, and an outpatient department generating about 1500 urine and 600 oral fluid drug screens per month; typically, fewer than 100 of the oral fluid screens have a simultaneously collected urine sample tested for comparison. Urine screens provide qualitative immunoassay results, and oral fluid tests provide quantitative LC-MS/MS results. Clarification of unexpected urine results is performed by LC-MS/MS at a reference laboratory after consultation between the ordering clinician and a laboratory director. The urine panel detects drugs prescribed for pain management as well as illicit drugs, and includes class-specific assays for benzodiazepines (BZ), buprenorphine (BUP), methadone (METHAD), opiates (OPI), and oxycodone (OXYCOD). The MR is the ratio of a drug metabolite concentration to its parent drug concentration, expressed as a range. A parent drug will have an MR for each of its main metabolites. …