After death, some micro-organisms produce ethanol of their own, so an alcohol concentration measured in a body does not always prove that the person had been drinking [1, 2]. That figure nonetheless weighs heavily on how the circumstances of a death are understood, particularly after a road traffic collision [2]. A review published in September 2026 in the International Journal of Legal Medicine takes stock of the specimens, markers and storage conditions that help separate genuine consumption from post-mortem production [1]. Its recommendations echo those set out by Olds and Jones in 2024 in the Journal of Analytical Toxicology, which add orders of magnitude useful to anyone who has to read a toxicology report [2].
Ethanol made by microbes after death
Within hours of death, gut bacteria spread into the vascular system and then to the organs [2]. Some of them, along with several yeasts, ferment whatever glucose remains and produce ethanol, much as in a wine vat [1, 2]. This post-mortem neoformation depends chiefly on the time elapsed before autopsy, the ambient temperature and the degree of putrefaction [2]. It is considered negligible when the autopsy takes place within 24 hours on a body showing no sign of decomposition, and in bodies recovered frozen [2]. It is more pronounced in heavily traumatised bodies, where open vessels expose blood to environmental microbes, and more so still after immersion in water or burning [2]. Road traffic victims, who often have multiple injuries, are therefore among those most exposed to this artefact, in cases where much hangs on the blood alcohol result [2].
The amount of available glucose also matters, which explains the attention paid to people with diabetes. Often hyperglycaemic at the time of death, they offer more substrate for fermentation, and neoformation may set in sooner [1, 2].
Usually low concentrations, occasionally high ones
The concentrations generated after death usually fall between 0.1 and 0.5 g/L of blood (0.01 to 0.05 g/100 mL), but values of 0.6 to 2 g/L have been reported [2]. A theoretical calculation gives a sense of scale, since a blood glucose of 1 g/L fermented in full would yield about 0.5 g/L of ethanol [2]. These orders of magnitude overlap the statutory drink-driving limits, which range from 0.2 to 0.8 g/L depending on the country [2]. In France, driving with 0.5 g/L of alcohol in the blood or more is a minor offence, and with 0.8 g/L or more a criminal one [6].
A high blood alcohol concentration in a putrefied body is not necessarily an artefact, however. In an autopsy series cited by Olds and Jones it mostly reflected genuine drinking, to which neoformation may have added 0.1 to 0.6 g/L [2]. These authors suggest, without claiming the force of a standard, raising the cut-off above which a post-mortem result is reported as positive from 0.1 to 0.2 g/L [2]. Where the body is obviously decomposed, they also propose subtracting 0.5 g/L from the mean result, a correction they acknowledge to be arbitrary and which massive trauma or high blood glucose may render insufficient [2].
Comparing blood with alternative specimens
Allane Patricia Santos da Paz and colleagues at the Federal University of Pará reviewed 10 years of literature, from 2014 to 2024 [1]. Of 414 articles identified in Scopus, Web of Science and PubMed, 54 studies were retained and used to draw up recommendations on collection, storage and interpretation [1]. Like earlier reviews, this one urges that a blood concentration should never be interpreted in isolation when the circumstances make production after death plausible [1, 2, 3]. Peripheral blood, drawn from the femoral vein before evisceration, remains the specimen of choice [1, 2]. Cardiac blood is more vulnerable, because ethanol still in the stomach at the time of death diffuses towards the heart, liver and lungs [2].
Vitreous humour, the fluid inside the eye, is the most useful complement. Remote from the gut and hard for bacteria to reach, it remains usable in a body that is already putrefied [1, 2].
It has its limits, notably after prolonged immersion or in a severely dehydrated body, from which it sometimes cannot be collected at all [1, 2]. Urine provides similar information, because it contains almost no glucose in healthy individuals and the intact bladder delays the arrival of bacteria [2]. That protection is lost in people with diabetes or a urinary tract infection, when yeasts such as Candida albicans find in the urine the sugar they need to ferment [1]. For badly degraded bodies, the review also mentions cerebrospinal fluid, preferably taken from the spinal canal, and matrices that are still exploratory, such as costal cartilage or the larvae of necrophagous insects [1]. Studies do not all agree on which matrix to favour in putrefaction, and some rank urine ahead of vitreous humour [1].
Interpretation then rests on whether the results are consistent. After genuine consumption, vitreous humour, which contains more water than blood, holds slightly more ethanol, with a mean ratio of 1.10 to 1.20 [2]. A positive blood result alongside negative urine or vitreous humour points instead to post-mortem production within the vascular compartment [2]. The 1989 explosion aboard the battleship USS Iowa illustrates the point, since of the 47 servicemen killed, 23 had a positive blood alcohol concentration, one of them at 1.9 g/L although neither his urine nor his bile contained measurable ethanol [2]. It would be unwise, on the other hand, to back-calculate a blood alcohol concentration from a vitreous or urine result, because the scatter between individuals is too wide [1, 2].
Looking for evidence of drinking before death
The second approach is to look for metabolites that glucose fermentation does not produce. Ethyl glucuronide (EtG) and ethyl sulphate (EtS) are formed in trace amounts when the body metabolises ingested alcohol, and their presence in blood, urine or vitreous humour is evidence of consumption before death [1, 2, 4].
EtG is the more sensitive of the two, but it can be degraded during putrefaction and disappear from badly decomposed blood, with a risk of false negatives [1]. EtS is more robust, including to heat, and less prone to being formed after sampling in infected urine [1, 2]. The Brazilian review regards it as the more reliable marker when the two disagree [1]. In a putrefied body, EtG is better measured in vitreous humour than in blood [1]. These markers call for two caveats. Their detection window, in urine especially, far exceeds that of ethanol, so a positive result establishes recent drinking without in itself establishing a blood alcohol concentration at the time of death [1]. Nor do they reveal how much of the measured concentration came from drinking and how much formed after death, since the two can add up in the same individual [2].
The laboratory also has indicators of microbial activity. The alcohols 1-propanol and 1-butanol, which micro-organisms produce alongside ethanol, cast doubt on the result when they appear on the chromatogram [2, 3, 5]. For that reason 1-propanol, the usual internal standard when blood from living subjects is analysed, is replaced by tert-butanol for autopsy specimens [2]. Acetaldehyde is harder to interpret, as it arises both from fermentation and from the oxidation of ethanol in a poorly preserved sample [1]. Only abnormally high concentrations, found together with higher alcohols, suggest neoformation, and some groups question the reliability of 1-propanol itself [1]. In urine, a raised ratio between two serotonin metabolites, 5-HTOL and 5-HIAA, likewise indicates drinking before death [2, 3].
Securing specimens from autopsy to analysis
Neoformation can continue in the tube after sampling, during transport and storage [1, 2]. Adding sodium or potassium fluoride at 1 to 2%, a higher concentration than in routine clinical tubes, inhibits glycolysis and curbs microbial activity [1, 2]. It should go into every specimen, vitreous humour and urine included [2]. Fluoride does not undo what happened in the body before autopsy, and it is less effective against yeasts such as Candida albicans [2]. Temperature matters just as much. Refrigeration at 4 °C is a minimum, and freezing becomes preferable beyond 48 hours of storage, at −20 °C in routine practice and down to −80 °C for long-term storage [1, 2].
The ethanol present in a sample can also fall over time, notably through oxidation to acetaldehyde, and all the more so when the tube is underfilled or has already been opened [1]. In fluoride-preserved autopsy blood frozen at −20 °C for 6 to 15 months, the mean decrease is of the order of 8 to 10% [2]. The stability studies compiled in the Brazilian review report losses of up to 15 or 16%, but several were carried out on blood from living subjects, whose stability is not necessarily that of autopsy blood [1, 2]. The authors accordingly recommend duplicate samples, in airtight tubes filled at least halfway, so that a never-opened specimen remains available for reanalysis [1]. These precautions are a matter of laboratory technique, yet they directly determine how much confidence can later be placed in the result.
The difficulty is that a result can be perfectly accurate analytically and still be hard to interpret in medico-legal terms.
A figure that has to be read in context
On 28 February 1975, a London Underground train failed to slow as it approached Moorgate station and ran on into a closed-off, unused section of track, killing 43 people including its driver [2]. His body was not recovered for 4 days, from a tunnel where the temperature had risen to 49 °C [2]. Blood taken from several sites gave concentrations of 0.2 to 0.8 g/L, and the figures reached the press before they had been interpreted, with no alternative specimen available to corroborate them [2]. The coroner’s jury returned a verdict of accidental death, and the crushing of the body, the heat, the delay and the fourfold difference between sampling sites all point to post-mortem production [2].
An overestimated post-mortem blood alcohol concentration can lead to a dead driver being wrongly held responsible and can deprive the next of kin of an insurance payout [2]. Conversely, genuine drinking can be underestimated if the sample deteriorated before analysis [1, 2]. Olds and Jones also point out that statutory driving limits were framed for blood drawn under sterile conditions from the living, and that an autopsy result should not be set against them without care [2]. The difficulty is that a result can be perfectly accurate analytically and still be hard to interpret in medico-legal terms. The laboratory determines precisely how much ethanol is present in the sample it receives. That does not answer another question, one that matters more to the investigation, namely where that ethanol came from.
When a post-mortem blood alcohol concentration is central to a case, judges, prosecutors and investigators therefore do well to look beyond the number. They need to know where the blood was drawn, what condition the body was in, whether vitreous humour or urine was analysed, how the tubes were stored, and whether EtG, EtS or putrefaction alcohols were looked for. For decomposed bodies, Olds and Jones suggest that the analytical report should itself state that some or all of the measured ethanol may have formed after death [2].
Références :
[1] da Paz A.P.S., Nunez L.B.B. Jr, de Mello V.J. Biological matrices for determining the origin of post-mortem ethanol, recommendations for collection and storage. International Journal of Legal Medicine, 2026, publié en ligne le 1er septembre 2026. DOI 10.1007/s00414-026-03994-9
[2] Olds M.L., Jones A.W. Preanalytical factors influencing the results of ethanol analysis in postmortem specimens. Journal of Analytical Toxicology, 2024, 48(1), 9-26. DOI 10.1093/jat/bkad078
[3] Lin Z., Wang H., Jones A.W., Wang F., Zhang Y., Rao Y. Evaluation and review of ways to differentiate sources of ethanol in postmortem blood. International Journal of Legal Medicine, 2020, 134(6), 2081-2093.
[4] Thierauf A., Kempf J., Perdekamp M.G., Auwärter V., Gnann H., Wohlfarth A., Weinmann W. Ethyl sulphate and ethyl glucuronide in vitreous humor as postmortem evidence marker for ethanol consumption prior to death. Forensic Science International, 2011, 210(1-3), 63-68. DOI 10.1016/j.forsciint.2011.01.036
[5] Vezzoli S., Bernini M., De Ferrari F. Ethyl glucuronide in vitreous humor and blood postmortem specimens, analysis by liquid chromatography-electrospray tandem mass spectrometry and interpreting results of neo-formation of ethanol. Annali dell’Istituto Superiore di Sanità, 2015, 51(1), 19-27. DOI 10.4415/ANN_15_01_05
[6] Direction de l’information légale et administrative. Alcool au volant. Service-Public.fr, fiche vérifiée le 11 juillet 2025.
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