Sensitive determination of ethyl glucuronide in serum and whole blood: detection time after alcohol exposure compared with urine

Objectives: Ethyl glucuronide (EtG) is a conjugated, minor ethanol metabolite used as a biomarker for recent alcohol intake. EtG is commonly measured in urine as part of a drug testing service but has also attracted attention for measurement in blood. However, due to lower EtG concentrations in blood, the detection time is expected to be shorter. The present work aimed to improve the analytical sensitivity of EtG in blood, to prolong the detection time. Methods: A liquid chromatography-tandem mass spectrometry method was developed for EtG in whole blood and serum, using protein precipitation with methanol, a deuterated internal standard, and selected reaction monitoring mode with negative electrospray ionization. No significant matrix effect was observed. The method generated linear results in the measuring range 1.0-50 mu g/L, the accuracy was within +/- 10% and the imprecision <15%. Results: In 46 patients followed with daily blood and urine sampling during alcohol detoxification, the mean (median) time to first negative serum EtG sample was 112 (111) h. This was slightly longer than for EtG in urine, using 100 mu g/Las cutoff. The detection rate was 76% for serum EtG and 68% for urine EtG. In cases where serum EtG was positive but urine EtG negative, the urine samples tended to be more dilute as indicated by lower creatinine concentrations. On admission to hospital, the whole-blood and serum EtG concentrations correlated with the breath ethanol concentration (p = 0.012 and p= 0.027, respectively). In 100 patients sampled at admission to hospital for other reasons than substance abuse and with no ethanol detected in breath, 40% tested positive for EtG in serum and 43% in urine. In 79 paired urine and serum EtG measurements, the median urine/serum concentration ratio was 155. Conclusions: A sensitive method was developed for EtG measurement in whole-blood and serum specimens, offering similar detection time for recent alcohol exposure compared with routine EtG measurement in urine.