Analysis of codeine positivity in urine of pain management patients

The opioids codeine and morphine have legitimate uses in managing chronic pain conditions, but they are frequently abused. Patients prescribed opioids submit urine samples for medication compliance monitoring, and the interpretation of the results is complex. The purpose of this study was to evaluate the percentage of codeine- and morphine-positive urine drug tests that result from morphine use only, with the positive codeine result arising from low levels of codeine present in pharmaceutical formulations of morphine. This study included 80 urine samples which tested positive for codeine and morphine after pre-analytical hydrolysis and analysis by gas chromatography-mass spectrometry. Quantitative results were correlated with patient prescription information and immunoassay results to classify patients into one of four categories: heroin users (50%), codeine users (34%), codeine and morphine users (5%), and morphine users (11%). The percentage of codeine-positive resulting from morphine use was higher than previous estimates. Urine from patients prescribed morphine only was found to contain codeine at <1% of the morphine concentration, a ratio that was also observed in patients who used heroin. Careful analysis of urine drug testing results, including assessing the ratio of codeine to morphine (C/M), can help providers determine if patients are compliant with their pain management regimens.