Ethanol can decrease during blood putrefaction as well as increase. In a 24-specimen experiment, Chen and colleagues observed different trajectories depending on the specimen and its starting condition. The results undermine a one-direction assumption that microbial activity always adds a predictable amount of ethanol.
What was incubated, and under which conditions?
The investigators selected 12 blood specimens from well-preserved deceased people and 12 from living people suspected of drunk driving. Each source contributed six classified as ethanol-negative and six classified as ethanol-positive, creating four groups of six specimens.
Autopsy blood came from the right cardiac chamber; living specimens were venous whole blood collected in sodium-citrate tubes. These differences in source and collection conditions were part of the design, rather than factors held identical between groups. The authors considered sterility during living-person collection a possible explanation for some observed differences.
Blood was incubated in closed tubes at 37°C without agitation and sampled on days 0, 1, 3, 5 and 7. The study’s initial casework handling involved immediate analysis or no more than eight hours at 4°C before testing, followed by −20°C storage. The seven-day incubation was a separate experimental condition. It did not simulate continuous refrigeration of routine preserved casework.
Initially negative blood could develop ethanol
In the ethanol-negative deceased group, three specimens showed continued ethanol increases across the seven-day experiment; the other three increased and then declined slightly. In the ethanol-negative living group, ethanol appeared by day 3 in five specimens, while specimen 14 remained at the reported 0.000 mg/mL throughout.
These different curves show why “ethanol formed in an incubated specimen” is more precise than assigning one production rate to every specimen. They also show that a final value can conceal an earlier peak.
Initially positive specimens often lost ethanol
The six ethanol-positive living specimens began between 0.379 and 1.041 mg/mL. The authors described an overall downward trend with fluctuations, except for specimen 23, whose ethanol was almost constant. In the ethanol-positive deceased group, starting concentrations and subsequent patterns were heterogeneous; the authors described decreases among higher-starting specimens but could not draw a uniform conclusion for low-starting specimens.
The report does not provide a validated rate of loss, a uniform percentage decrease or a statistical comparison establishing that every positive specimen must decline. Its individual curves should not be converted into a back-calculation formula for an unrelated death investigation.
A changing concentration is a net result
The authors discussed ethanol–acetaldehyde conversion and microbial production or degradation as explanations. They did not identify the microbial species in each experimental specimen or separately measure the amount produced and the amount consumed. A falling ethanol concentration therefore does not prove that no ethanol formation occurred at the same time.
That distinction also prevents the reverse error: an ethanol increase does not prove that no ethanol was lost. The measured concentration reflects the balance of processes in that particular specimen and incubation history.
Other markers did not supply a correction
Dual-column headspace GC–FID measured ethanol, acetaldehyde and n-propanol. Their stated detection limit was 0.002 mg/mL and quantification limit 0.005 mg/mL; ethanol calibration extended to 3.0 mg/mL. EtG and EtS were measured separately by LC–MS/MS, with limits of 10 and 15 ng/mL for detection and quantification.
Acetaldehyde changed during incubation, but the investigators could not fit a satisfactory quantitative relationship to ethanol. N-propanol was undetected in many specimens. Neither result justified a case-specific correction for the ethanol change.
What this means for serial testing
Retain the complete sequence of results and the time–temperature history, rather than selecting one measurement as necessarily representative of the original specimen. Reanalysis can document disagreement, but its direction alone cannot reconstruct ethanol at collection or during life.
The small groups, unequal starting concentrations, absent microbial identification and single warm-incubation temperature limit generalization. The study neither establishes impairment nor assigns a causal role in death. Compare this controlled incubation with the distinct evidence from a preserved autopsy specimen whose ethanol increased during serial testing.
Primary source
Chen X, Dong X, Zhu R, et al. Abnormally High Blood Acetaldehyde Concentrations Suggest Potential Postmortem Ethanol Generation. Journal of Analytical Toxicology. 2021;45:748–755. doi:10.1093/jat/bkaa173.
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