Blood acetaldehyde above 0.14 mg/mL can support suspicion of postmortem change, but it does not prove that all detected ethanol formed after death. Chen and colleagues proposed that threshold from selected forensic samples and laboratory incubation experiments. Their study did not validate a case-specific calculation of the amount of ethanol produced.
The threshold came from three selected groups
The investigators initially collected 177 venous whole-blood samples from living people suspected of drunk driving and 250 right-cardiac-chamber blood samples from deceased people. Living specimens were collected into sodium-citrate tubes. Autopsy specimens were collected into glass tubes for prompt analysis without the preservation treatment that could interfere with the later putrefaction experiment.
Samples were analyzed immediately or refrigerated at 4°C for no more than eight hours before testing, then stored at −20°C. The deceased group included traffic fatalities and other causes of death. Some case-specific death times and postmortem intervals were unavailable.
For the cross-sectional comparison, blood with ethanol below 0.05 mg/mL was excluded: 12 living samples and 138 autopsy samples. The resulting groups were 165 living people, 90 deceased people whose bodies were well preserved, and 22 with heavy putrefaction. The well-preserved bodies had been deeply frozen at approximately −20°C; that body history is distinct from laboratory storage of a collected tube.
Higher group concentrations did not create a diagnostic test
Mean acetaldehyde concentrations were 0.101 ± 0.101 mg/mL in the living group, 0.117 ± 0.093 mg/mL in the well-preserved deceased group and 0.506 ± 0.429 mg/mL in the heavily putrefied group. Values are reported as mean ± standard deviation.
The living and well-preserved deceased groups did not differ significantly (P = 0.062). The well-preserved and heavily putrefied groups did differ significantly. Those findings support an association with specimen or body condition in this selected dataset; they do not establish that acetaldehyde has only one source.
The authors selected 0.14 mg/mL—equivalent to 0.014 g/dL—slightly above the approximately 0.134 mg/mL upper confidence bound reported for the well-preserved group. A confidence interval for a group mean is not a reference interval covering individual people. The paper did not establish sensitivity and specificity for that threshold against independently known amounts of postmortem ethanol.
Why a numerical subtraction is unsupported
The study also incubated 24 blood specimens at 37°C for seven days: six each from ethanol-negative deceased people, ethanol-positive deceased people, ethanol-negative living people and ethanol-positive living people. Acetaldehyde and ethanol changed over time, but attempts to fit a quantitative relationship between them were unsuccessful.
The cross-sectional analysis likewise found no significant correlation between acetaldehyde and ethanol concentrations in the three groups. A high acetaldehyde result therefore cannot be converted into a validated quantity of ethanol to subtract from the reported blood concentration.
Measurement limits and preservation remain relevant
Acetaldehyde, ethanol and n-propanol were measured by dual-column headspace GC–FID. The stated detection and quantification limits for all three were 0.002 and 0.005 mg/mL. Calibration extended from 0.005 to 0.5 mg/mL for acetaldehyde and n-propanol, and to 3.0 mg/mL for ethanol. These are analytical limits, not boundaries separating ingestion from microbial activity.
EtG and EtS were measured separately by LC–MS/MS, with detection and quantification limits of 10 and 15 ng/mL. Their presence can contribute evidence about antemortem exposure, but does not establish that every ethanol molecule in the collected specimen came from drinking.
Use the result as one part of the investigation
The study lacked other-matrix measurements, identification of the microbes involved and complete timing information for every case. Initial concentrations also varied substantially between experimental specimens. Its proposed threshold warrants contextual interpretation, not automatic classification.
Review collection site, body condition, preservation, storage, paired specimens and biomarkers together. The distinction between analytical uncertainty and possible formation is developed in our discussion of ethanol assay uncertainty. Acetaldehyde detection alone establishes neither impairment nor ethanol as a cause of death.
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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