What are direct ethanol biomarkers?

Direct ethanol biomarkers are the products of direct ethanol biotransformation and represent unequivocal evidence of alcohol exposure. Examples are ethyl glucuronide (EtG) and ethyl sulfate (EtS), which are produced from phase II liver metabolisms of ethanol; phosphatidylethanol (PEth), which is generated by the reaction catalyzed by phospholipase D of phosphatidylcholine with ethanol; and fatty acid ethyl esters (FAEEs) resulting from esterification of fatty acids and ethanol.

Which non-traditional matrix types can labs test for direct ethanol biomarkers?

Urine and whole blood are the traditional specimen types used to probe for recent ethanol ingestion or exposure. Recently, however, non-traditional matrix types such as hair, nail, and dried blood spots (DBS) have emerged as valid alternatives that offer advantages such as longer detection windows and ease of specimen collection. Meconium and umbilical cord have also been exploited for identification of prenatal alcohol exposure; however, numerous studies have demonstrated the limited utility of neonatal matrices and shown that the suggested test cutoffs for determining prenatal alcohol exposure are inconsistent.

What are the detection windows for ethanol biomarkers in non-traditional matrix types?

Ethanol, EtG, and EtS in whole blood are cleared within hours, and EtG and EtS in urine are cleared within 1–5 days. However, longer detection windows are needed in cases associated with repeated binge drinking or with subjects at risk of developing an alcohol use disorder. Generally, PEth in whole blood as well as in DBS is specific for binge drinking during the past 2–4 weeks, while EtG in hair and fingernails is specific for repeated binge drinking in the last 1–3 months. FAEEs in hair have also been considered as a marker for chronic alcohol use. However, the Society of Hair Testing consensus states that use of ethanol-containing hair care products may lead to false-positive results.

What are the advantages of collecting hair, nail, and DBS compared with urine and whole blood?

While urine is a specimen at high risk of adulteration, hair, nail, and DBS can be directly inspected for sample validity (i.e., the absence of cosmetic treatments and/or artificial hair/nail) at the site of collection.

Although studies have shown that whole blood and DBS are equivalent in terms of PEth analysis, the latter also have several advantages over whole blood, including ease of collection and the small amount of sample needed. Most important, DBS are not susceptible to false-positive results due to post-collection synthesis of PEth when ethanol is still present in the blood.

What are the disadvantages of non-traditional matrices?

Non-traditional matrices that retain ethanol biomarkers for lengthened periods of time cannot provide pharmacokinetic information, such as the time of the patient’s last alcohol use, the amount of ethanol ingested during the last drinking episode, or the frequency of alcohol intake.

Moreover, although these matrices’ minimal sample collection requirements are beneficial, they come with several trade-offs: high-sensitivity instrumentation is needed to detect the minute amounts of analyte in small specimen aliquots, the original specimen must be maintained and stored for further investigation, and there is a high risk of receiving a specimen amount that is insufficient for testing.

What are the applications for direct ethanol biomarkers in non-traditional matrices?

Tests for EtG in hair and nail and PEth in DBS are now routinely performed by laboratories such as the United States Drug Testing Laboratories, Inc., and are frequently requested by law enforcement or health insurance agencies. Typical clients include agencies re-issuing driver’s licenses to individuals repeatedly convicted for driving under the influence, and health programs evaluating the performance of professionals serving the public, such as airline pilots and surgeons.

Irene Shu, PhD, DABCC (CC, TC), is assistant laboratory director at the United States Drug Testing Laboratories, Inc. Email: irene.shu@usdtl.com