An EtG alcohol test measures ethyl glucuronide, a substance formed as the body breaks down alcohol. EtG is a direct alcohol biomarker, meaning that it reflects alcohol metabolism rather than an indirect effect on an organ or blood measurement. EtG and a related marker, ethyl sulfate, or EtS, are usually measured in urine.
The distinction between alcohol and an alcohol biomarker matters. A test for EtG looks for a product of alcohol breakdown rather than measuring alcohol itself. SAMHSA's 2012 advisory describes these breakdown products as measurable for longer than alcohol remains measurable in blood or urine. The advisory discusses EtG as a tool used to monitor abstinence in clinical and justice settings. That describes a use of the test, not a conclusion about an individual result.
An EtG result needs context because the source of exposure may be uncertain. The advisory notes that alcohol in everyday products can contribute to positive results. The presence of EtG therefore does not, by itself, establish that a person drank an alcoholic beverage. The advisory also describes alcohol biomarkers as complementary to a patient history and other information rather than substitutes for that information.
The analytical method is another distinction. The 2012 advisory states that analysis should use gas or liquid chromatography with mass spectrometry and that enzyme immunoassay produces a fairly high number of false positives. It calls for confirmation of a positive immunoassay result by those more accurate methods. Confirmation concerns the analytical finding. It does not remove the separate question of how the alcohol exposure occurred.
This overview explains the marker and its limitations. It does not interpret a personal result, prescribe a testing schedule, select a cutoff, or establish whether a particular test meets an employment or court requirement.
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