3. LC-MS/MS Reveals High False Positive Rate of Ethylglucuronide Immunoassay in a Pain Management Population
Tue 12:06 PM - PosterSplash Track 1
Bridgit Crews
Millennium Laboratories
Bridgit Crews, Charles Mikel, Robert West, Sergey Latyshev, Perla Almazon, Amadeo Pesce

Millennium Laboratories, Inc.
Ethyl glucuronide (EtG) and ethyl sulfate (EtS) have been identified as sensitive biomarkers of alcohol consumption due to their extended window of detection compared to ethanol. EtG may be degraded or synthesized in vitro in the presence of certain bacteria, therefore EtG testing should always be accompanied by EtS testing. Current immunoassay screen for EtG have questionable sensitivity and accuracy and only detect EtG.

Using a multiplexed LC-MS/MS platform (Thermo Fisher Scientific) we developed a high throughput “dilute and shoot” assay to quantitate both EtG and EtS. The multiplexed system operates with an injection-to-injection cycle time of 1 minute, with lower limits of quanitation of 500ng/mL and 100ng/mL for EtG and EtS, respectively. This high throughput capability allows for specific and accurate quanitation of EtG and EtS in over 1,000 patient urines per day on a single instrument.

We observed a high rate of false positive immunoassay results confirmed by a negative result by LC-MS/MS. These observations were validated by a reference laboratory. We also observed that more than 4 % of specimens contained a high concentration of ethyl sulfate accompanied by a negligible concentration of ethyl glucuronide and produced a negative screening result by immunoassay. These results highlight the need to validate immunoassay results in specific patient populations.