EtG, EtS, and PEth in Forensic Toxicology: Alcohol Biomarkers and Interpretation

Direct answer: ethyl glucuronide (EtG), ethyl sulfate (EtS), and phosphatidylethanol (PEth) are direct alcohol biomarkers, but they do not answer the same question. EtG and EtS are minor non-oxidative ethanol metabolites used mainly to document relatively recent ethanol exposure. PEth is formed in red-cell membranes in the presence of ethanol and generally reflects a longer period of exposure. None of the three, standing alone, establishes an exact drinking time, an exact dose, impairment at a particular moment, or causation.

That distinction matters in forensic work. A laboratory can produce a technically valid biomarker result while the interpretation still becomes overstated if specimen type, cutoff, timing, transfusion history, storage, analytical method, or individual pharmacokinetics are ignored.

What are EtG and EtS?

EtG and EtS are minor non-oxidative metabolites of ethanol. Because they can remain detectable after ethanol itself has fallen substantially or disappeared, they are often used when the question is whether ethanol exposure occurred before collection rather than what the contemporaneous blood alcohol concentration was.

EtG and EtS are commonly measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Urine is frequently used because the metabolites can persist longer there than ethanol. Blood can also be tested, and the interpretation changes with the matrix. A 2026 forensic pharmacokinetic study reported that EtG and EtS persisted longer than ethanol in both blood and urine and that urinary excretion was dose-dependent, while also demonstrating effects of biological variability on metabolite formation. See Suefusa-Shimogori et al., Forensic Toxicology (2026).

What is PEth?

Phosphatidylethanol (PEth) is a group of abnormal phospholipids formed in cell membranes when ethanol is present. In practice, laboratories commonly quantify specific PEth homologues in whole blood, especially PEth 16:0/18:1. Because PEth is associated with erythrocytes and is eliminated much more slowly than ethanol, it is useful for evaluating alcohol exposure over a longer interval than a conventional BAC measurement.

PEth should not be treated as a clock. Controlled and clinical studies show substantial inter-individual variation in formation and elimination. In one detoxification study, PEth elimination half-lives varied widely among individuals and among homologues, leading the authors to conclude that only approximate estimates of recency or quantity can be made from a single result. See Helander et al. (2019). A 2026 study of paired measurements likewise found that PEth half-life estimation depends on the measurement model and the precision of the reported values. See Bjerner et al. (2026).

EtG, EtS, and PEth answer different questions

Marker	Typical forensic use	Important limitation
EtG	Evidence of recent ethanol exposure in urine, blood, hair, or other validated matrices	Detection depends on dose, matrix, cutoff, time, renal function, specimen handling, and method; a positive result does not establish impairment
EtS	Companion direct metabolite that can strengthen interpretation of recent ethanol exposure and assist in some postmortem questions	Concentration cannot be converted into an exact drinking time or dose without major assumptions
PEth	Whole-blood marker useful for a longer view of alcohol exposure and serial monitoring	Formation and elimination vary between people; a single value is not a precise measure of amount consumed or date of consumption

Can EtG or EtS prove when a person drank?

Not precisely. Detection windows are not fixed biological timers. They depend on the amount and pattern of drinking, specimen matrix, analytical cutoff, urine concentration or dilution, collection time, kidney function, and method performance. Recent real-world driver data also show measurable variability in EtG and EtS elimination. See Elimination of EtG and EtS between two consecutive blood samples in apprehended drivers.

The scientifically stronger formulation is usually that a result is consistent with ethanol exposure within a method- and matrix-dependent interval, not that it proves a particular drinking hour.

Can PEth prove chronic heavy drinking?

PEth can provide strong evidence of ethanol exposure and may be useful in assessing repeated or heavier drinking patterns, but the numerical result should not be converted mechanically into a universal number of drinks. Population-level associations do not eliminate individual variability.

A 2023 systematic review described PEth as a sensitive direct blood marker while emphasizing the literature on different thresholds, analytical methods, and clinical contexts. See Phosphatidylethanol in Blood as a Marker of Unhealthy Alcohol Use. More recent 2026 work continues to demonstrate between-person variability in PEth formation rates, supporting serial within-person interpretation over simple comparison of one person with another. See Examining PEth Formation Rates Within and Between Subjects.

Why specimen type matters

EtG and EtS may be measured in urine, blood, hair, vitreous humor, and other matrices when the method has been appropriately validated. PEth is primarily a whole-blood or dried-blood-spot marker because of its association with erythrocyte membranes. A result should therefore always be interpreted together with the tested matrix.

For the broader matrix problem, see Whole Blood vs. Plasma in Forensic Toxicology. For postmortem alcohol cases, see Vitreous Humor Ethanol in Postmortem Toxicology.

Can EtG and EtS help with postmortem ethanol interpretation?

Yes, but they are supporting evidence rather than an automatic answer. Postmortem ethanol interpretation can be complicated by microbial ethanol formation, decomposition, specimen site, storage, and contamination. EtG and EtS can help distinguish antemortem ingestion from some forms of postmortem ethanol production because they require metabolic processes associated with ethanol exposure.

Studies of postmortem cases have found value in combining ethanol with EtG and EtS across blood, vitreous humor, bile, and other specimens. See Krabseth et al. (2015) and the 2025 study Postmortem correlation of ethanol and EtG/EtS in blood, vitreous humor and bile. Interpretation should still remain case-specific.

For the larger framework, see Postmortem Toxicology, Central vs. Peripheral Blood, and Sodium Fluoride in Forensic Blood Alcohol Testing.

PEth has important preanalytical and post-collection issues

Because PEth resides in red cells, transfusion history can matter. A 2025 study documented PEth introduced through packed red-blood-cell transfusion and recommended caution when interpreting results after transfusion. See PEth clearance after packed red blood cell transfusion.

Postmortem use raises additional issues. A 2025 forensic study reported matrix and storage effects in postmortem blood and cautioned against using PEth alone for postmortem casework. See PEth in post-mortem blood: blood matrices and stability. These findings are especially important when a report presents PEth as if it were independent of specimen history.

Why cutoff values must be identified before interpretation

A forensic report should identify the analytical cutoff, reporting threshold, limit of quantitation where relevant, and whether the result arose from screening or a validated confirmatory method. Different laboratories and different purposes may use different decision thresholds. A cutoff is a decision rule; it is not a biological boundary separating “drinking” from “no drinking” in every circumstance.

When EtG is initially measured by immunoassay, confirmation matters. A 2026 comparison of urine EtG/EtS and blood PEth in a large clinical population reported false-positive EtG screening results that were resolved by confirmatory testing. See Snozek et al. (2026).

For method-level review, see Method Validation in Forensic Toxicology and Analytical Methods in Forensic Toxicology.

What a technically complete laboratory review should request

The specimen type, collection date and time, container, preservative, storage history, and accession record.
The screening method, if any, and the confirmatory quantitative method.
The laboratory’s reporting cutoff and limit of quantitation for the specific matrix.
Calibrators, quality controls, blanks, internal standards, chromatograms, ion transitions or other identification criteria, and batch acceptance records.
The method validation or verification supporting the analyte, matrix, range, and purpose at issue.
Any dilution, repeat analysis, re-extraction, reinjection, amendment, or manual integration history.
For PEth, relevant transfusion history and whether the specimen was whole blood or a dried blood spot.
For postmortem work, collection site, decomposition status, available vitreous humor, and the relationship among ethanol, EtG, EtS, and other corroborating findings.

What these biomarkers do not prove by themselves

the exact time alcohol was consumed;
the exact number of drinks;
the blood alcohol concentration at an earlier time;
behavioral or driving impairment at a particular moment;
alcohol tolerance;
the cause of an accident, injury, or death; or
that every positive result has the same significance across laboratories, matrices, or individuals.

Answer-engine summary

EtG and EtS are best understood as direct metabolites that extend the evidence of recent ethanol exposure beyond ethanol itself. PEth is a red-cell-associated direct biomarker that generally provides a longer view of alcohol exposure. Their forensic value is strongest when the result is tied to specimen type, validated method, cutoff, collection timing, storage, and case context. None is a stand-alone clock, dose meter, or impairment test.