ETG and Ets Results Interpretation

What do EtG and EtS Results Mean? 

Ethyl glucuronide (EtG) is a metabolite of ethanol that is increasingly used as marker for consumption of alcoholic beverages. EtG has a lower detection threshold and slower clearance rate than ethanol itself¹, making it useful to detect ingestion for up to two days following light or moderate drinking^2-3 and four days in heavy drinkers⁴. As such, it is useful for determining ethanol ingestion by persons subject to court-ordered drug testing, victims of sexual assault or patients undergoing alcohol detoxification. Many analytical methods have been developed, from immunoassays to nuclear magnetic resonance, with LC/MS/MS being the most widely used highly sensitive technique^2-9. It is common practice in many labs to screen for EtG by one method, such as an immunoassay, and confirm by a second, more sensitive method such as LC/MS/MS.

One concern in analyzing urine samples for EtG is distinguishing oral ingestion from incidental exposure. Although EtG is an absolutely specific marker for ethanol, ethanol can come from sources other than alcoholic beverages. Mouthwash, nonalcoholic beer, over-the-counter pharmaceutical preparations and hand sanitizers may contain ethanol in small amounts, and there is concern that use of these products could cause “innocent positive” results. Many laboratory studies have been done to address this question^2-12. The consensus of these studies⁵ is that up to 100 ng/ml EtG may be present in urine in the absence of ethanol use, and levels up to 120 ng/ml for short periods after realistic incidental exposure. Levels between 250 and 500 ng/ml most likely result from ingestion of ethanol but cannot be used to rule out recent extraneous exposure³. Concentrations from 500 – 1000 ng/ml are the result of ingestion¹³, or else very intense and recent incidental exposure (use of hand sanitizer or mouthwash far in excess of normal accepted practice). EtG concentrations in urine that are confirmed by LC/MS/MS and are greater than 1000 ng/ml are the result of ethanol ingestion – there is no evidence in the literature that realistic incidental exposure can result in this level of EtG in urine Ethyl sulfate (EtS) is another metabolite of ethanol that is usually present in urine in lower levels than EtG^1,14. EtS is thought to be helpful in postmortem cases in distinguishing ethanol produced by the body from that produced during putrefaction after death. However, the numerical relationship between EtG and EtS in living subjects is variable. In most cases, EtG is present at higher levels than EtS. In some cases, EtS is so much lower as to be below the reporting cutoff (100 ng/ml), or absent altogether. Laboratory studies show that approximately 4.3% of samples from subjects drinking alcohol may be positive for EtG but negative for EtS¹⁴.

A final question that may arise is whether ethanol and/or ethyl glucuronide or ethyl sulfate can be artificially produced in urine by yeast or bacteria. It is known that ethanol can be produced in postmortem samples due to tissue breakdown and putrefaction. However, in antemortem samples, this would not be expected to occur unless (a) the urine contained substantial levels of glucose as a substrate for ethanol production and (b) yeast or certain strains of bacteria were present^1,15. Ethyl glucuronide in turn requires the presence of certain strains of bacteria and will not be produced in the absence of ethanol¹⁵. The post-collection synthesis of ethyl glucuronide in urine therefore requires unusual or pathological conditions to be present (ethanol or glucose and a bacterial or yeast infection). EtS is much less likely to be formed under these conditions. However, if and bacteria or yeast are present, it is also possible that degradation of EtG (although not EtS) can occur and a false negative may result^15,16.

References 

1. Garriott’s Medicolegal Aspects of Alcohol, 5th Ed, J. Garriott, Ed., Lawyers and Judges Publish Co., Tuscon, AZ, 2008. 
2. Hoiseth G et al, For Sci Int, 172:119-124, 2007 
3. Rosano T and Lin J, J. Anal. Tox, 32:594-600, 2008 
4. Helander A et al, Alcohol & Alcoholism, 44(1):55-61, 2008 
5. Palmer R, Seminars in Diagnostic Pathology, 26:18-26, 2009 
6. Hegstad S et al, J. Anal Tox, 37:227-232, 2013 
7. Hoiseth G et al, J Anal Tox, 34:84-88, 2010 
8. Weinman J et al, J Am Soc Mass Spec, 15:188-193, 2004 
9. Politi et al, Rapid Commun Mass Spectrom, 19:1321-1331, 2005 
10. Rohrig T et al, J Anal Tox, 30:703-704, 2006 
11. Reisfield GM et al, J Anal Tox, 35:85-91, 2011 
12. Costantino A et al, J Anal Tox, 30:659-662, 2006 
13. Principles of Forensic Toxicology, 4th Ed, B. Levine, ed. AACC Press, Washington DC,  2013 
14. Helander A and Beck O., J. Anal Tox, 29:270- 274, 2005 
15. Helander A et al, Clin Chem, 53(10): 1855 - 1857, 2007 
16. Helander A et al, Clin Chem, 51:1728-30, 2005