EtG Testing for Alcohol Abstinence
The question we are asked most frequently, year after year for 30+ years, is “How long after drinking can alcohol be detected?” The answer we give has always been based on the assumption that a breath alcohol or saliva test device will be used to detect the presence of alcohol in the blood. When the alcohol has been eliminated from the body (in two to 20+ hours, depending on how much alcohol the individual has had to drink) a breath or saliva test can no longer detect the alcohol. The relatively short window of detection for blood alcohol makes it difficult to effectively monitor abstinence with a breath or saliva test unless an individual is tested at least once a day.
EtG (Ethyl Glucuronide) is a direct metabolite of ethyl alcohol and has a half-life of two to three days, much longer than ethyl alcohol. EtG has long offered hope for a more effective way to monitor abstinence. For example an EtG test administered on a Monday could confirm that an individual abstained from alcohol use over the weekend, something that a breath alcohol test cannot do.
Negative EtG Results Confirm Abstinence
Even though EtG testing has been around for at least ten years it is still a relatively new alcohol testing methodology. SAMHSA (Substance Abuse and Mental Health Services Administration) issued two advisories on EtG testing, the first in 2006 and most recently in 2012. The advisory makes it clear that SAMHSA does not believe that a positive EtG test by itself is sufficient to definitively identify an individual who consumed alcohol. However, a negative EtG test gives convincing evidence that an individual did not consume alcohol for one or two days prior to testing.
What About Positive EtG Test Results?
As we noted above, SAMHSA does not recommend that an agency use a positive EtG test as stand-alone evidence that an individual consumed alcohol. They recommend that there be additional corroborating evidence of alcohol use to support a positive EtG test. This could be the individual’s own admission of alcohol use or confirmation with another testing methodology. The reason for this position is that incidental contact with products that contain alcohol – such as mouthwash, hand sanitizers, etc. – can result in a positive EtG test. A high cut-off level of at least 500 ng/mL should rule out incidental contact as the cause for a positive test, but SAMHSA still believes there should be corroborating evidence of alcohol use.
In spite of the recommendation not to use positive EtG results as a definitive indicator of alcohol consumption, the 2012 SAMSHA Advisory does include the following preliminary guidance on what positive results may indicate.
>1,000 ng/mL:
– Heavy drinking on the same day or previously (e.g., previous day or two).
– Light drinking the same day.
500–1,000 ng/mL:
– Previous heavy drinking (previous 1–3 days).
– Recent light drinking (e.g., past 24 hours).
– Recent intense “extraneous exposure” (within 24 hours or less).
100–500 ng/mL:
– Previous heavy drinking (1–3 days).
– Previous light drinking (12–36 hours).
– Recent “extraneous” exposure
On-site EtG Testing
Until very recently EtG testing could only be accomplished in a laboratory. In the past year several manufacturers introduced instant tests for EtG. As with all tests of this type, instant tests are designed to give preliminary results; presumptive positives should be confirmed with a laboratory. As of this writing in July 2015 none of the instant EtG tests have received FDA clearance, but are for forensic use only in corrections and law enforcement.