Blood to serum concentration ratios for ethyl glucuronide and ethyl sulfate after five drinking episodes

Ethyl glucuronide (EtG) and ethyl sulfate (EtS) are mostly analyzed in urine; consequently, most kinetic studies are based on urine samples. In forensic cases, however, it may be necessary to determine these alcohol biomarkers in serum, whole blood, or capillary blood. While there are sufficient data on EtG and EtS in serum after alcohol consumption, the amount of data available on whole blood concentrations is small. Therefore, data on corresponding blood-to-serum ratios seem to gain importance. This study provides data on a drinking experiment with 5 drinking episodes, where serum and whole blood samples were taken simultaneously from 11 healthy participants over 10 days. The samples were analyzed for EtG, EtS, and ethanol. EtG and EtS analysis in whole blood and serum were performed by liquid chromatography-tandem mass spectrometry; ethanol was determined by gas chromatography-flame ionization detection and an alcohol dehydrogenase-based method. EtG and EtS reached their maximum concentration 4-7 h after alcohol consumption. For EtG, a mean blood-to-serum ratio of 0.58 with a range from 0.38 to 0.73 was found; for EtS, the mean ratio was 0.81 with a range from 0.61 to 0.92, indicating a predominant distribution in the serum. For both analytes, high correlation coefficients were obtained when plotting concentrations in serum against concentrations in whole blood. Concerning elimination profiles of the individuals, no time or concentration dependence of EtG or EtS blood-to-serum ratios could be deduced. Neither for EtG nor for EtS was a regularity of curve progressions observed in our test specimens.