EVIDENCE LIBRARY
Can PEth Form After Blood Collection? Why a Dried Blood Spot Is Not Always Artifact-Free
Can PEth form after a blood draw? A 2021 LC-MS/MS study found PEth artifacts in wet blood and some dried-blood devices, but not open filter cards.
Yes. Phosphatidylethanol (PEth) can be produced inside an ethanol-containing blood sample after collection, and drying a blood sample does not always prevent it. In a controlled laboratory study, PEth 16:0/18:1 formed in liquid whole blood and in three commercial volumetric dried-blood microsampling devices after researchers added ethanol to previously PEth-negative specimens. Conventional open filter-paper blood spots did not show measurable formation under the tested conditions. A phospholipase D inhibitor prevented detectable new formation in the tested systems. The immediate forensic question is therefore not just whether a PEth laboratory reported a concentration, but when and under which collection, drying, transport, and inhibition conditions that concentration arose.
This is a specimen-integrity question, not a universal argument that PEth testing is unreliable. PEth is a useful marker of alcohol exposure, but an analytically identified PEth molecule cannot, by its identity alone, reveal whether it formed before or after the specimen left the person.
What does a PEth blood test actually measure?
Phosphatidylethanols are ethanol-derived phospholipids produced in membranes through an enzymatic reaction involving phospholipase D (PLD), ethanol, and phosphatidylcholine. The 2021 experiment by Beck and colleagues measured one specific molecular species, PEth 16:0/18:1, by liquid chromatography–tandem mass spectrometry (LC–MS/MS). It did not measure total PEth across every molecular species, and it did not use PEth as a direct breath- or blood-ethanol assay.
These distinctions matter. A measured PEth concentration is a laboratory finding in a biological specimen. Interpreting it as a history of consumption involves biological formation and elimination, a known collection and handling process, the method’s reporting limit, and the particular person. PEth does not measure contemporaneous intoxication, reaction time, divided attention, driving skill, or accident causation. See the related guide to specimen collection and matrix integrity.
What question did the 2021 PEth experiment investigate?
Beck, Mellring, Löwbeer, Seferaj, and Helander (2021) examined whether PEth could form after blood had been drawn and whether different microsampling formats changed that risk. Their starting material was de-identified surplus venous whole blood, including samples that tested negative for PEth. For the experimental challenges, researchers added ethanol to a final concentration of 2 g/L. That was a controlled specimen-spiking condition, not a measured BAC in volunteers who had consumed an alcoholic beverage.
They compared room-temperature storage of wet blood, conventional Whatman 903 open filter-paper spots, and three volumetric dried-blood devices: Mitra Clamshell, HemaXis DB 10, and Capitainer qDBS. Investigators also tested PLD inhibitors, particularly sodium metavanadate, in treated prototype sampling materials. Their LC–MS/MS quantification limit for the PEth analyte in liquid whole blood was 0.01 μmol/L. Results below that limit must be described as below the study’s quantification threshold, not proof that zero molecules existed.
Did dried blood spots prevent PEth formation?
That depended on the device. During a 48-hour room-temperature challenge using PEth-negative blood fortified with 2 g/L ethanol, the standard open filter-paper card showed no quantified new PEth. All three commercial volumetric microsampling formats showed post-sampling formation in at least some specimens. The wet blood kept in test tubes also showed formation. The devices were not interchangeable merely because each ultimately contained dried blood.
| Sample format | Samples with detected new formation | Reported concentration range | Forensic reading |
|---|---|---|---|
| Wet blood in test tubes | 20 of 20 | 0.03–0.08 μmol/L | PEth may continue forming after collection in ethanol-containing liquid blood. |
| Open Whatman 903 filter-paper card | 0 of 20, by the tested quantification limit | Below 0.01 μmol/L | This open-card format suppressed detectable formation under these conditions. |
| Mitra Clamshell device | 8 of 20 | 0.02–0.12 μmol/L among specimens showing formation | Some volumetric dried-blood samples remained susceptible. |
| HemaXis DB 10 device | 13 of 20 | 0.04–1.04 μmol/L among specimens showing formation | Device and drying behavior mattered in this laboratory challenge. |
| Standard Capitainer qDBS device | 20 of 20 | 0.83–2.02 μmol/L | The largest observed formation among these device formats occurred in this specific configuration. |
| Capitainer qDBS prototype with PLD inhibitor | 0 of 20, by the tested quantification limit | Below 0.01 μmol/L | Inhibitor treatment prevented quantified new formation in the tested prototype. |
These are experimentally ethanol-fortified specimens, not prevalence estimates or device failure rates in routine casework. The reported concentrations are newly measured PEth, not blood ethanol, breath alcohol, or an amount of drinking. The figures describe the study’s tested materials and conditions and cannot be applied as correction factors to unrelated specimens.
Why is a dried blood spot not automatically artifact-free?
The paper suggests that drying speed and evaporation of residual ethanol are important. A conventional filter-paper card exposes a thin drop of blood to air; a volumetric collection device can hold the blood within a structure that dries differently. In the experiment, investigators observed less formation on qDBS filter discs removed from their holders than on the intact devices. That pattern supports a drying-related explanation, but the experiment does not establish that drying time was the sole causal mechanism in every device.
A sample’s label, therefore, is insufficient. A laboratory report describing a specimen as a “dried blood spot” should still be linked to the actual collection system and its validated handling protocol. The exact device, its treated or untreated status, the period before complete drying, temperature, and whether ethanol was present all bear on what can reasonably be inferred.
Could a PEth-negative sample become quantifiably PEth-positive after collection?
Under these controlled conditions, yes. At the beginning of one qDBS experiment, samples from two donors were below the PEth reporting threshold. After addition of ethanol and three hours of room-temperature drying in the intact device, their PEth 16:0/18:1 results reached 0.22 and 0.17 μmol/L, respectively. Those numbers reflect formation inside spiked specimens, not real-world drinking by the donors during the experiment.
This result is important because it demonstrates a mechanism for a misleading result if a case specimen retained ethanol and its collection system allowed PLD activity to continue. But it does not demonstrate that every unexpected clinical or forensic PEth result is an artifact. The study did not determine how frequently this occurs in routine laboratories, which person experienced it, or how much of an individual reported value arose after collection.
What did the PLD inhibitor experiments establish?
The researchers tested agents intended to block the enzyme involved in PEth synthesis. Among the alternatives evaluated, sodium metavanadate (NaVO3) was selected for further experiments. In the tested dismounted discs and inhibitor-treated prototype qDBS devices, newly formed PEth stayed below the quantification threshold under the reported conditions. The inhibitor was present before the blood challenge; the study does not show that adding a chemical later can erase an artifact that has already formed.
| Experiment | Observation | Proper evidentiary limit |
|---|---|---|
| Two initially PEth-negative donors; untreated intact qDBS; 3 hours | New PEth measured at 0.22 and 0.17 μmol/L after 2 g/L ethanol challenge | Demonstrates formation in these two stored laboratory specimens; not a population error rate. |
| Ten ethanol-spiked specimens; standard qDBS; 3 hours | Quantified formation in 8 of 10, ranging 0.01–0.36 μmol/L | Response varied between specimens, even with a common challenge. |
| Ten ethanol-spiked specimens; inhibitor-treated qDBS; 3 hours | New PEth below 0.01 μmol/L in the tested specimens | Pre-treatment prevented quantified formation under those conditions. |
| Four PEth-positive specimens; qDBS without versus with inhibitor | After ethanol addition, untreated results averaged 142% of starting PEth; inhibitor-treated averaged 101% | Existing PEth can be inflated by additional formation; 142% is not a universal correction multiplier. |
The last comparison is especially instructive: the error mechanism is not limited to turning an initially negative specimen into a measurable one. A specimen that already contains PEth may acquire more PEth during handling if ethanol remains and PLD is active. Neither direction nor magnitude can be presumed for another specimen without case-specific validation and records.
How should a forensic laboratory review an unexpected PEth finding?
An effective review follows the specimen chronologically. It establishes the precise PEth analyte and reported units; whether the submitted material was venous liquid whole blood, a filter-paper spot, or a specific volumetric microsampling system; and when that material was collected, transported, dried, refrigerated, frozen, extracted, and tested. It also seeks the contemporaneous evidence of ethanol in the specimen and whether the collection system used a validated PLD-inhibition procedure.
Next, the reviewer examines the laboratory’s actual analytical validation and batch records: PEth species identification, extraction conditions, calibration, lower quantification limit, controls, uncertainty or imprecision, and relevant specimen-stability studies. The analyst should distinguish analytical identification of PEth from a proposition about when PEth formed. A repeat measurement of an archived sample can confirm what that sample contains at retesting without automatically reconstructing its concentration at collection.
General method and chain-of-custody concepts are addressed in blood alcohol analytical methods and the site’s forensic toxicology evidence library. Blood ethanol by headspace GC and PEth by LC–MS/MS answer different analytical questions; results from one method should not be silently substituted for the other.
Does this study prove that a positive PEth result is false?
No. It proves that post-collection formation is possible in particular ethanol-containing specimen systems. It does not adjudicate whether a particular positive result reflects drinking, contamination, in-tube formation, a mixture of pre-existing and newly formed PEth, or some other explanation. Nor does it establish how often this artifact arises in a properly validated contemporary testing service.
The paper used surplus blood experimentally fortified with a fixed ethanol concentration and monitored selected storage conditions. It was not a prospective study of defendants, employees, treatment participants, crash-involved drivers, or the performance of all marketed sampling systems. One author disclosed involvement with a device company, underscoring the value of independently reviewing the specific experimental configurations rather than generalizing the findings to an entire technology category.
Can a PEth concentration establish alcohol impairment or the cause of an event?
Not by itself. PEth is an indirect alcohol-exposure biomarker, and its concentration is affected by biological formation, elimination, analytical method, and specimen integrity. The Beck experiment neither measured laboratory psychomotor task outcomes nor evaluated driving performance, clinical intoxication, accident reconstruction, or an individual’s behavior at a particular time. It supplies no scientifically validated person-specific formula translating a disputed PEth number into BAC, number of drinks, impairment, or proximate cause.
Those are separate evidentiary propositions. The distinction between an assay result, a sample-handling artifact, an inferred exposure history, and a functional or legal conclusion should be maintained throughout expert analysis.
Frequently asked questions about PEth sampling artifacts
Can PEth increase after the blood draw?
Yes, if the specimen contains ethanol and PLD remains active. Beck and colleagues directly observed post-sampling formation under laboratory challenge conditions. The magnitude for a specific patient sample cannot be deduced from those experiments alone.
Does a dried blood spot always prevent new PEth formation?
No. Open Whatman 903 filter-paper spots did not show quantifiable formation in this study, but three commercial volumetric dried-blood devices did under the same 2 g/L ethanol challenge. The device and drying procedure matter.
Did the study show a measurable difference between sampling devices?
Yes, in the tested laboratory samples. After 48 hours, newly measurable PEth appeared in 8 of 20 Mitra, 13 of 20 HemaXis, and 20 of 20 standard qDBS samples. These are not validated real-world false-positive rates.
What does sodium metavanadate do in this experiment?
It inhibited the PLD-dependent reaction that otherwise generated new PEth in ethanol-containing sampled blood. In the tested inhibitor-treated devices, newly formed PEth was below the study’s quantification limit. Use in any actual laboratory must follow that laboratory’s own validated procedure.
Can a later retest reveal exactly how much PEth was present at collection?
Not necessarily. A retest can measure the current sample, but a collection-time value cannot automatically be recovered if PEth formed or degraded during intervening handling. Any retrospective estimate would require independently justified specimen-specific evidence.
Does 2 g/L ethanol represent the BAC of every person tested?
No. The researchers deliberately added ethanol to laboratory specimens to study mechanism. It was not a clinical BAC measurement of the donors, and the findings do not apply quantitatively to every ethanol concentration or handling history.
Does this evidence prove someone was sober, drinking heavily, or impaired?
No. The experiment concerns PEth formation in stored samples, not an individual person’s drinking chronology, current psychomotor ability, or the cause of an incident. A forensic opinion requires the validated assay, specimen record, and relevant independent evidence.
Primary scientific source and scope
Beck O, Mellring M, Löwbeer C, Seferaj S, Helander A. Measurement of the alcohol biomarker phosphatidylethanol (PEth) in dried blood spots and venous blood—importance of inhibition of post-sampling formation from ethanol. Analytical and Bioanalytical Chemistry. 2021;413:5601–5606. doi:10.1007/s00216-021-03211-z.
Bottom line: The same PEth analyte can be generated by the biological pathway after the sample is collected if ethanol and active PLD remain. Some collection formats suppressed the artifact in this experiment and others did not. The forensic task is to establish the specimen-specific conditions and avoid turning a valid chemical identification into an unsupported conclusion about a person’s drinking history, impairment, or causation.