How does an EtG test work?

An EtG test works by detecting ethyl glucuronide, a metabolite produced when the body processes alcohol. Unlike breath or blood alcohol tests that measure ethanol directly, EtG testing identifies a byproduct formed after alcohol metabolism has begun. Because ethyl glucuronide remains in the body longer than ethanol itself, EtG testing can detect alcohol exposure after alcohol is no longer measurable in breath or blood.

When alcohol is consumed, most ethanol is broken down through standard metabolic pathways in the liver. A smaller portion is converted into ethyl glucuronide through a separate biochemical process involving glucuronidation. This metabolite is then excreted primarily through urine, where laboratory analysis can identify its presence.

EtG testing is most commonly performed using urine samples, although other biological specimens may also be analyzed in some settings. Detection sensitivity depends on laboratory cutoff thresholds, the amount of alcohol consumed, metabolism, hydration, and the timing of testing. Larger or repeated alcohol exposure generally produces higher metabolite concentrations.

Because EtG reflects alcohol metabolism rather than immediate intoxication, it is often used to evaluate recent alcohol exposure over an extended detection period. Breath and blood testing are more closely associated with current impairment, while EtG testing focuses on identifying whether alcohol consumption occurred within the prior several days.

Laboratory interpretation considers both metabolite concentration and testing context. Low-level EtG findings may occasionally result from incidental alcohol exposure involving certain products containing alcohol, although testing thresholds are often designed to reduce this possibility. Confirmation testing and clinical context are therefore important when evaluating EtG results.