Gas chromatography ("GC") / mass spectrometry ("MS") is a method that identifies the specific presence of particular substances within a given sample.
Ethyl glucuronide (EtG) is a direct metabolite of alcohol (ethanol). Its presence in urine may be used to detect recent ethanol ingestion, even after ethanol is no longer measurable. The presence of EtG in urine is an indicator that ethanol was ingested.
In addition to EtG, recent scientific studies have identified ethyl sulfate (EtS) as a second specific metabolite or biomarker of ethanol. For this reason, RTL tests and reports EtS, in conjunction with EtG, to confirm recent ethanol ingestion or exposure. The detection of EtG and EtS offers greater sensitivity and accuracy for determination of recent ethanol ingestion, than by detection of either biomarker alone.
The sweat patch consists of a gauze pad covered by a protective membrane similar to that of a band-aid. The membrane has an adhesive perimeter that sticks tightly to the test subject's skin. The sweat patch is usually worn on the subject's upper arm. Before application, the subject's arm is swabbed with an isopropyl alcohol rub.
After the patch has been worn for approximately seven to ten days, it is removed and the gauze pad is sent to the laboratory for testing. The lab usually performs "screening tests" for several different drugs, using an immunoassay testing system. If any screening test indicates the presence of a drug, the lab performs a "confirmatory test" for that drug, using the more precise "gas chromatography / mass spectrometry" (GC/MS) testing system. If the confirmatory test finds levels of the drug above the "cutoff" the lab is using, the lab will report a positive test result.
Each trial court has the right to make its own decision as to whether sweat patch evidence will be admitted, and how that evidence will be used. A decision by an appellate court would govern the trial courts in that appellate court's jurisdiction, but so far there are no appellate court decisions on the sweat patch from either state or federal courts.
Many trial courts have considered the sweat patch. Some courts have admitted sweat patch evidence, and relied on it in deciding to imprison probationers or terminate parental custody. Others have found the sweat patch insufficiently reliable for these purposes: at least six different federal courts have rejected government efforts to base punitive action on sweat patch test results.
While Drug Policy Alliance tracks court decisions on the sweat patch, many of these cases are confidential, and hardly any have resulted in written court decisions. There is no exhaustive list of court rulings on the sweat patch. Only two courts have issued written decisions that discuss the science behind the sweat patch and are published in official legal case reports.