EVIDENCE LIBRARY
What Can a 36-Report Audit Establish About Alcohol-Absorption Assumptions?
An audit found a two-hour post-absorptive assumption in all 36 reviewed reports. It examined reporting practice, not the subjects’ actual absorption curves or the error in each calculation.
A report audit can reveal a repeated assumption, but it cannot establish that every calculation using that assumption was wrong. In an original review of 36 forensic retrograde-extrapolation reports, Aaron Olson found that all assumed post-absorptive status within two hours. The audit did not independently measure the subjects’ absorption curves or determine the true earlier BAC in those cases.
That distinction matters when evaluating DUI expert reports. Documentation of an assumption, evidence that the assumption was justified, and proof of the resulting numerical error are three different questions.
What the author actually reviewed
The paper examined 36 reports from the Minnesota Bureau of Criminal Apprehension toxicology section, authored during 2023–2024 and obtained through a government data request. The author assessed whether they assumed absorption within two hours and whether they considered food, medication, medical conditions, trauma or possible delayed absorption.
According to the paper, all 36 used the post-absorptive assumption within two hours. None documented consideration of medications, food or medical conditions in the audit’s table. One mentioned trauma and the possibility of delayed absorption.
These counts describe the supplied reports and the author’s assessment of their contents. They are not measurements from 36 controlled drinking experiments, and they do not establish how often all forensic laboratories use the same approach.
Why the assumption affects the calculation
A simple retrograde estimate adds an assumed elimination amount to a later measured alcohol concentration. That arithmetic represents elimination over the intervening period; it does not independently estimate continuing absorption.
If a person was still absorbing alcohol during the relevant interval, applying an elimination-only calculation can overstate the earlier concentration. The site’s general guide to retrograde BAC extrapolation explains those assumptions. The audit adds a narrower question: how explicitly did these particular reports address them?
The paper’s discussion draws on other research about delayed absorption. That literature provides reasons to examine case circumstances, but it does not prove that delayed absorption occurred in any one of the audited cases.
What the audit does not prove
A report may omit a factor because it was unknown, absent, addressed elsewhere or not considered. The published audit does not resolve all those possibilities. Lack of discussion in a report is therefore evidence about the report, rather than direct evidence that a particular physiological condition existed.
Likewise, a conventional timing assumption can be insufficiently explained without necessarily producing an incorrect result in that case. To quantify error, one would need an independently supported earlier concentration or suitable evidence about the person’s actual concentration–time course.
The audit provides no case-by-case series of independently established earlier BACs against which to calculate numerical bias. It cannot supply a percentage of wrongful results, a universal correction or a conclusion about a particular prosecution.
How to use the finding in a case review
The useful application is to inspect what a report states and what the underlying record supports. Identify the last-drink time and its source, the measurement and collection times, the specimen or breath method, and the factual basis for assuming absorption was complete.
If food, medication, gastrointestinal disease or trauma is relevant, determine whether there is evidence that it applied to the person and occasion. Their general capacity to influence kinetics does not establish the direction or magnitude of an effect in the case.
Serial measurements may help characterize a trend, but even a declining interval must be interpreted in relation to the earlier period being estimated. A measured blood value, serum/plasma result and breath concentration also require distinct treatment; the audit does not eliminate those matrix differences.
Scope and limitations
This was a small, single-agency document audit without a demonstrated representative sampling frame for all forensic practice. It did not report an independent physiological assessment of each subject or a blinded multi-reviewer assessment of the reports. The author disclosed providing forensic toxicology testimony.
The paper also discusses professional recommendations and emerging medication questions. This article does not treat those discussions as a statement of current law or establish a medication-specific absorption adjustment. The primary audit supports a conclusion about documentation and assumptions, not a universal biological timetable.
For a distinct uncertainty question, see why calculated BAC uncertainty depends on the case inputs. A precise-looking final number remains conditional on the facts and model used to produce it.
Primary source
Olson A. Extended absorption, implications: Rethinking alcohol pharmacokinetics in forensic calculations. Medico-Legal Journal. 2026;94:24–27; first published 2025. https://doi.org/10.1177/00258172251382701.