EVIDENCE LIBRARY
Can One Drinking Episode Push PEth Above 20 ng/mL? A 12-Person Trial
A controlled 12-person trial found PEth above 20 ng/mL after one drinking session. Examine serum BAC, dried blood spots, assay limits and forensic uncertainties.
Short answer: Yes. In a controlled study of 12 adults, one supervised alcohol-drinking episode produced a maximum phosphatidylethanol (PEth 16:0/18:1) concentration above 20 ng/mL in 9 of 12 participants during the first trial and 7 of 12 during the second trial. The finding matters when a PEth result is used to assess reported abstinence: crossing 20 ng/mL does not, by itself, distinguish a single drinking event from a repeated pattern of drinking, establish the time or amount consumed, or prove impairment.
The evidence comes from Spleis and colleagues’ controlled-drinking study, published online in 2024 and in the 2025 volume of the International Journal of Legal Medicine. The researchers measured PEth in dried blood spots after two scheduled alcohol exposures. They did not establish a universal dose-to-PEth conversion rule or a validated person-specific method of reconstructing drinking history.
What did the 12-person drinking study actually show?
The investigators recruited 12 healthy adult volunteers, six women and six men. Participants first underwent a four-week abstinence period. They then completed two supervised vodka-drinking sessions separated by at least nine days. The alcohol doses were calculated to target BAC values of 0.6 g/kg in the first session and 0.75 g/kg in the second, but these values were planned targets, not measured outcomes.
The mean reported BAC, measured at a specified point after drinking, was 0.56 g/kg in the first trial and 0.67 g/kg in the second. In both sessions, every participant ultimately had a maximum PEth 16:0/18:1 concentration above the study’s quantification limit of 10 ng/mL. Yet the number exceeding 20 ng/mL differed: nine participants in the first trial and seven in the second. A higher target dose therefore did not create a simple, monotonic increase in the number crossing this threshold.
These are controlled laboratory observations in a small group, not a clinical validation of a universal threshold or a legal classification rule. One person contributing to two sessions is not equivalent to two independent people, and the study included no placebo-drinking comparison group.
What were the alcohol doses and measured concentrations?
Participants drank 37.5% alcohol by volume vodka mixed with juice. The individualized quantities were estimated with the Widmark formula and consumed over 30 minutes in the first session and 45 minutes in the second. The participants had been instructed to finish their most recent meal at least two hours before the session.
| Study measure | Trial A | Trial B | Interpretation |
|---|---|---|---|
| Participants | 12 | 12 | The same study cohort underwent both exposures. |
| Widmark-calculated BAC target | 0.60 g/kg | 0.75 g/kg | Prospective dose calculation; not an assay result. |
| Reported BAC 45 minutes after drinking ended | Mean 0.56 g/kg; range 0.47–0.68 | Mean 0.67 g/kg; range 0.53–0.87 | Obtained from a venous specimen analyzed after separation of serum by headspace GC-FID. |
| Maximum PEth > 20 ng/mL | 9/12 (75%) | 7/12 (58%) | Trial-specific observed counts, not an estimated population sensitivity. |
| Highest individual maximum PEth | 28.8 ng/mL | 44.9 ng/mL | Capillary/venous dried-blood-spot PEth 16:0/18:1 by LC-MS/MS. |
Source: Spleis et al., original Results and Table 2. Concentrations are reported using the study’s units; grams per kilogram must not be silently replaced with grams per liter or breath alcohol units. The source describes a venous blood collection but specifies that the ethanol determination used centrifuged serum. The resulting reported BAC is not interchangeable with a separately tested whole-blood ethanol concentration without method- and conversion-specific information.
Which specimens and analytical methods were involved?
Three fundamentally different measurements occurred. The PEth biomarker was measured in dried blood spots (DBS), primarily capillary fingertip blood deposited on paper cards, with an additional DBS made from the venous draw. A specific PEth homolog, 16:0/18:1, was quantified using liquid chromatography–tandem mass spectrometry (LC-MS/MS). The reported limit of detection (LOD) was 5 ng/mL and the limit of quantification (LOQ) was 10 ng/mL.
A venous specimen was collected 45 minutes after the end of drinking. The laboratory separated serum and used headspace gas chromatography with flame-ionization detection (HS-GC-FID) to measure ethanol. The investigators also monitored breath alcohol at repeated intervals and measured urine ethyl glucuronide (EtG) and ethyl sulfate (EtS) by LC-MS/MS as part of their protocol. The initial urine EtG/EtS tests before the drinking sessions were negative.
| Question | Actual specimen / method | What it cannot independently establish |
|---|---|---|
| Was PEth formed after drinking? | DBS PEth 16:0/18:1; LC-MS/MS; LOD 5 ng/mL, LOQ 10 ng/mL. | Exact ethanol dose, drinking frequency, current impairment or event-specific behavior. |
| What ethanol concentration was reported during the session? | Venous draw, centrifuged serum; HS-GC-FID; reported BAC in g/kg. | Maximum lifetime BAC, the entire absorption curve or a person’s later BAC. |
| Was ethanol monitored while participants remained onsite? | Serial breath-alcohol monitoring. | A direct blood-ethanol assay or a universal breath-to-blood relationship. |
| Did screening support the study’s predose conditions? | Urine EtG/EtS by LC-MS/MS before each exposure, plus earlier PEth assessments. | Perfect verification of every intervening hour of abstinence. |
Specimen distinction is indispensable in forensic testimony. A biomarker generated in blood following ethanol exposure is not the ethanol molecule itself. A measured biomarker concentration is therefore not a BAC, and a single BAC measurement at a scheduled time is not a complete pharmacokinetic history.
Can one drinking episode raise PEth above the 20 ng/mL threshold?
In this study, yes. The lowest reported alcohol concentration associated with a maximum PEth exceeding 20 ng/mL was a measured BAC of 0.48 g/kg. This does not make 0.48 g/kg a necessary, sufficient, or generally applicable threshold. Other participants did not cross 20 ng/mL despite higher observed BAC values, and PEth formation reflects interindividual and analytical variation.
Likewise, the finding that every observed BAC greater than 0.7 g/kg was associated with a maximum PEth above 20 ng/mL is confined to the small number of observations in this study. It is not a prediction rule validated in a representative population.
A positive biomarker result can therefore be evidence of ethanol exposure without establishing a habitual consumption pattern. Conversely, a concentration below the selected cutoff must not be represented as proof that no alcohol was consumed. The 20 ng/mL interpretive value discussed by the authors arose in a particular German abstinence-monitoring context; it is not a universal legal definition of drinking, abstinence or impairment.
When did PEth reach its observed maximum?
The researchers collected multiple DBS samples after drinking, including a spot prepared from the venous draw and later self-collected fingertip spots. Across the 24 drinking-session observations, maximum PEth was recorded at the venous-draw DBS in 13 observations (54%); at another sample on the drinking day in six; and on the following day in five. The first recorded maximum therefore often occurred early, but not invariably at the same time for everyone.
The phrase observed maximum matters. Sampling was discrete, not continuous, so the precise biochemical peak could occur between collections. Moreover, some later spots were collected by participants at home, and the authors excluded a few individual implausible PEth results. Those features restrict precision about exact peak time.
At day one after the first session, all participants but one had fallen below 20 ng/mL; after the second session, three participants still had concentrations above 20 ng/mL on day three. The results support variable persistence under this dosing and sampling schedule, not a promise that a given person’s result must become negative by a fixed hour or day.
Why did fewer people exceed the threshold after the higher targeted dose?
The study reported 9/12 above 20 ng/mL after the lower target and 7/12 after the higher target. That superficially counterintuitive pattern should not be recast as evidence that more alcohol reduces PEth. The targets were calculated before drinking, actual achieved concentrations differed, and the investigators identified individual variability and laboratory measurement uncertainty as potential explanations.
Crucially, the two sessions were conducted in the same people with only a minimum nine-day separation. Some pre-second-session PEth values were still measurable rather than uniformly zero. The study did not randomize dose order or isolate each exposure using entirely independent participant groups. Thus a paired comparison is informative but does not justify a person-specific dose–response equation or population prevalence estimate.
The authors reported an expanded measurement uncertainty of 29.2% (coverage factor k = 2) for the PEth method. This is a laboratory uncertainty statement, not a standardized estimate of each individual’s entire biological variation. It reinforces the need to avoid treating a value slightly on either side of 20 ng/mL as an infallible boundary between two entirely different behaviors.
Does a PEth result establish how much or how often a person drank?
No precise reconstruction follows from this trial. PEth 16:0/18:1 is an exposure-related molecule produced in the presence of ethanol, and its concentration depends on formation, elimination, time since drinking, sample handling, and participant-specific factors. The investigators observed that even identical target protocols did not yield uniform concentrations or identical detection windows.
A single PEth value by itself does not discriminate whether the signal arose from one episode or several episodes. Two values drawn at known intervals may add information about a trend, but the trend still cannot automatically reveal exact consumed grams, the precise hour of use, or the legal significance of the event. Interpretation should be anchored to the sampled matrix, exact homolog, laboratory cutoff, result uncertainty, specimen collection time, and independent case facts.
Nor should the term abstinence marker be misunderstood. The marker can be useful in monitoring exposure, but its detection is not equivalent to direct observation of drinking, and a negative result below a threshold is not synonymous with proof that no drinking occurred. These are different propositions.
Could a PEth test prove alcohol impairment on a particular occasion?
No. This experiment did not administer a standardized driving examination, field sobriety test, eyewitness procedure, divided-attention battery or event-specific cognitive assessment. PEth formation occurred after drinking but was not calibrated as an impairment score. The measured serum-ethanol result at one timepoint likewise does not, by itself, establish functional impairment or a person’s conduct at another time.
To evaluate impairment or legal causation, the underlying evidence must address the relevant date, activity, chronology, analytical matrix and behavioral observations. A clinician’s diagnostic conclusion, an instrument concentration, a biomarker classification and a legal element are not interchangeable forms of proof. The study offers no threshold linking PEth 16:0/18:1 to an individual’s driving performance, reaction time, responsibility for a collision or credibility.
What limitations matter most in a forensic challenge?
Small, selected sample. Twelve apparently healthy adults are not a representative cross-section of drivers, patients, people with liver disease, or individuals in court-ordered abstinence programs. Sampling variability becomes substantial when a reported fraction is 7/12 or 9/12.
Two exposures in one cohort. These are 24 session observations, not 24 independent volunteers. They do not represent a blinded, randomized comparison of groups receiving only one dose.
Nonzero baseline in some samples. A four-week initial abstinence phase and negative urine screens strengthen the design, yet some DBS baseline values before the second session were measurable. Treating every second-session maximum as if PEth necessarily began at zero would overstate isolation of the second exposure.
Collection and analytical uncertainty. Some DBS spots were self-collected at home, the authors noted potential effects of fingertip compression, and the PEth method carried an expanded measurement uncertainty of 29.2%. The source also notes removal of several implausible individual sample values.
Limited temporal sampling and outcome scope. One scheduled venous ethanol sample per drinking event and discrete DBS timepoints cannot reveal a complete individual BAC curve or exact PEth peak. No real-world impairment, last-drink truthfulness, accident or case-specific causation endpoint was tested.
How should a toxicologist review a disputed PEth result?
A disciplined analysis starts with the original laboratory record, not a general article or a cutoff cited without context. Identify the PEth homolog and measured value, whether the matrix was a fingerstick DBS or venous whole blood, the analytical method and validation, the limit of detection and quantification, reported measurement uncertainty, quality controls, specimen age and storage, and whether repeat collections are actually comparable. Determine exactly which definition of a positive result was used and in which jurisdiction or monitoring protocol.
Next separate the laboratory finding from the competing factual assertions. A measured positive PEth may support prior ethanol exposure. It does not independently prove a particular beverage, exact amount, repeated use, time of consumption, impairment at an incident, violation of a particular policy, or intentional dishonesty. Such assertions require their own evidence and may remain indeterminate.
Related same-site context is available in our guides to specimen collection and matrix integrity, blood ethanol analysis by headspace GC-FID, and pharmacokinetic interpretation. Those guides provide background; the PEth study and the original case records control any particular scientific claim.
Frequently asked questions
Can PEth exceed 20 ng/mL after only one drinking session?
Yes, it did in 9 of 12 participants after the first supervised session and 7 of 12 after the second. These observations show that a result above 20 ng/mL is not uniquely diagnostic of repeated drinking.
Did all 12 participants test positive for PEth?
Each had an observed maximum PEth 16:0/18:1 exceeding the assay’s quantification limit of 10 ng/mL after each study event. That is not the same as all 12 exceeding the separate 20 ng/mL interpretive threshold.
Did the investigators actually attain their target BACs?
Not uniformly. Mean reported values were 0.56 g/kg and 0.67 g/kg, below their respective planned 0.60 and 0.75 g/kg targets. The target was calculated from the anticipated dose rather than directly measured in advance.
Does a PEth of 21 ng/mL categorically prove a violation of abstinence?
No scientific conclusion about a particular monitoring violation follows from the number alone. The applicable policy, method, uncertainty, matrix, sample history and other evidence must be evaluated. The study’s 20 ng/mL criterion came from a particular interpretive context.
Can a negative PEth exclude a drinking episode?
Not necessarily. A report below a cutoff can reflect many circumstances, including timing, amount, individual response and the selected reporting threshold. This trial did not validate a rule that an individual who drinks must cross 20 ng/mL.
Can a dried-blood-spot PEth result be converted into a precise BAC?
No validated individual conversion was established here. PEth is a formed lipid biomarker, while BAC represents ethanol concentration in a specified biological matrix at a specified time. They are different analytes with different kinetics.
Does PEth prove a person was impaired while driving?
No. The study measured ethanol and PEth under supervision but did not assess driving, functional impairment or accident causation. Those conclusions require additional event-specific evidence.
Primary scientific source
Spleis F, Bantle M, Schuldis D, Bell LM, Thierauf-Emberger A, Weinmann W. Detection of phosphatidylethanol after ethanol intake with targeted blood alcohol concentrations of 0.6 g/kg and 0.75 g/kg. International Journal of Legal Medicine. 2025;139:589–596. Published online December 4, 2024. doi:10.1007/s00414-024-03379-w.
This article summarizes one original human drinking experiment and does not substitute for the complete scientific paper, an individual laboratory validation file, expert evaluation or case-specific records.