Proper Use of EtG/EtS Testing

EtG and EtS are both metabolites of alcohol and result from enzyme activity, enzymes that are determined genetically. People vary widely as to the activity of these enzymes, explaining why some people have variations in the presence and ratio of EtG to EtS and vice versa. (For example, humans have over 15 possible variants of beta-glucuronidase, the enzyme that turns alcohol into EtG). Additionally, it has been shown that bacteria can occasionally destroy EtG but not EtS. Both ETG and ETS are similar and detect the same thing (alcohol exposure) with the approximate same timeline of detection. They are often run together because of people's variations in enzymes and because of the bacteria issue and so running both results in better accuracy. If either or both are positive, drinking should be suspected and it indicates a positive screening test for alcohol. Everyone being tested for EtG/EtS should be informed to avoid all products containing alcohol to avoid "incidental exposure." If either of these tests are positive at any level then recent consumption of ethyl alcohol is possible and statistically likely but occasionally positives occur from "incidental exposure" but this is less likely if people avoid incidental alcohol exposure.  Raising cutoffs values can decrease detection of "incidental exposure" but this also decreases the sensitivity of the tests for detecting drinking. If someone tests positive for EtG and/or EtS they should be confronted in a supportive manner because they likely have been drinking. If they deny drinking and confirmation of drinking is desired then a phophotidyl ethanol (PEth) test should be performed on blood. PEth testing confirms drinking because it only becomes positive after about 7 standard drinks, more than is possible from any form of incidental exposure. So, the only reason to raise cutoffs (EtG > 100ng/ml and/or EtS > 25ng/ml) is to decrease the  number of false positives. The reason to keep the cutoffs low is to decrease false-negatives.  Now that a confirmation test, PEth. is available, the ideal situation is to have the lowest possible cutoffs for EtG/EtS and if the person denies drinking then perform a PEth test. If it is positive it confirms drinking.