Improved detection of ethyl glucuronide and ethyl sulfate in a pain management population using high-throughput LC-MS/MS.

Background: Ethyl glucuronide (EtG) and ethyl sulfate (EtS) have been proposed as markers for detecting alcohol use because they exhibit extended excretion lifetimes when compared with ethanol; however, their presence is not considered as absolute proof of alcohol use. Two methods are currently used for the detection and quantitation of EtG: immunoassay and mass spectrometry. The purpose of this study was to provide more patient data to better compare the two methods.

Methods: A retrospective diagnostic accuracy study was performed to compare the methods. EtS was also measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) as an additional comparative analyte. The investigators examined 4,287 sequential urines from pain patients to determine the incidence of alcohol use and the corresponding presence of EtG by immunoassay at a cutoff of 500 ng/mL. EtG and EtS were subsequently quantitated in all the urines using LC-MS/MS.

Results: A total of 794 samples were found positive by immunoassay, and these results were compared at three distinct LC-MS/MS cutoffs of 100, 500, and 1,000 ng/mL. The incidence of ethanol use in this population was found to be at least 12 percent.

Conclusions: Approximately 30 percent of the samples screened by immunoassay as positive were confirmed to be negative by LC-MS/MS.