Comparison of an automated and point-of-care immunoassay to GC-MS for urine oxycodone testing in the clinical laboratory

Abstract

OxyContin®, a controlled-release formulation of oxycodone, is increasingly abused. Monitoring patient compliance by urine drug testing may deter illegal diversion of OxyContin. Two urine immunoassays were evaluated with a 100 ng/mL cutoff for oxycodone. The Microgenics Corporation Oxycodone DRI on the Bayer ADVIA 1650 and a point-of-care (POC) immunoassay, Monitect Oxycodone POC from Branan Medical Corporation, were compared to gas chromatography-mass spectrometry (GC-MS) with a detection limit of 50 ng/mL free oxycodone. Between-day precision for DRI yielded coefficients of variation from 3.9% to 7.0% at 75 and 125 ng/mL. Fifty-two positive and 52 negative urines were tested. The DRI had a 100% agreement with GC-MS. Two positive specimens had free oxycodone < 50 ng/mL, but oxycodone metabolites, oxymorphone and oxycodone glucuronide > 100 ng/mL, were identified by GC-MS analysis. The POC assay had two false positives and 15 indeterminate (±) results. Codeine or hydrocodone was present in all but one of these samples. There was no interference with DRI from morphine, codeine, hydrocodone, hydromorphone, dihydrocodeine, or 6-monoacetyl morphine. Four-hundred and ninety urine samples were subsequently tested with DRI to estimate the oxycodone-positive rate at our hospital, and 47 (9.4%) were positive. The confirmation rate with GC-MS for free oxycodone, not including metabolites, was 93%. The Microgenics DRI offers good performance for oxycodone urine testing and is a better choice for the clinical laboratory than the POC assay. Confirmation of screened positive samples requires a method that can detect total oxycodone and oxymorphone.