Do Two Blood Alcohol Samples Measure a Driver’s Liver Elimination Rate?

Not necessarily. Two blood samples establish a change in measured blood alcohol over an interval; they do not automatically isolate the rate at which the liver metabolized alcohol. In a 1990 study, Neuteboom and Jones examined paired samples from suspected impaired drivers and warned that some very steep calculated declines could reflect distribution between blood and tissues rather than liver metabolism alone.

This distinction matters when a rate calculated from two later samples is applied backward to estimate BAC at driving. The observed interval and the earlier period are different evidential questions.

The study began with 2,354 paired-sampling cases

The investigators reviewed Dutch forensic laboratory records from February 1982 through September 1987. Among 209,661 submitted blood samples, 2,354 cases involved blood collection on two occasions from the same suspect.

At each collection, two tubes were filled consecutively from a cubital vein. These duplicate tubes should not be confused with the two collection times used to calculate the concentration change. The blood contained heparin and sodium fluoride, and ethanol was measured using an alcohol-dehydrogenase method, with duplicate assays by two laboratory workers.

The calculated rate was the first BAC minus the second BAC, divided by the elapsed time in hours. This is an average concentration slope between two observations, rather than a direct measurement of hepatic alcohol processing.

Filtering the records changed the rate distribution

The main analysis used 1,314 paired-sampling cases with collection intervals of 10–40 minutes. The investigators separately considered very short intervals, small concentration differences and longer delays.

In particular, pairs differing by less than 0.05 mg/mL were set aside. That is 0.005 g/dL. Removing small changes necessarily limits what the remaining distribution can establish about nearly flat concentration profiles.

The restricted analysis reported a mean apparent disappearance rate of 0.22 mg/mL per hour, equivalent to 0.022 g/dL per hour. Its reported range was 0.10–0.64 mg/mL per hour, or 0.010–0.064 g/dL per hour. The authors explained that the lower end reflected their selection rules. It should not be treated as a demonstrated minimum elimination rate for every driver.

The largest slopes were not established as liver-metabolism rates

The authors questioned whether the highest calculated rates could represent hepatic metabolism. Continuing redistribution and equilibration between blood and tissue water could affect the concentration in sampled blood.

A short interval also makes any concentration difference large when expressed as an hourly rate. As an arithmetic illustration, a difference of 0.010 g/dL over ten minutes produces a slope of 0.060 g/dL per hour. This example is a calculation, not an additional observation from the study and not a physiological elimination constant.

The distinction does not require rejecting both laboratory measurements. Even accurate measurements can describe a concentration trend influenced by more than one biological process. Analytical uncertainty and the accuracy of recorded collection times add separate issues to an individual calculation.

Rising and nearly flat results require their own interpretation

In the original 2,354-case dataset, 47 cases—approximately 2%—showed a rising BAC. The authors interpreted this as evidence of continuing absorption at sampling. That observation concerned the blood-draw interval, not the earlier moment of driving or arrest.

The separately considered small-difference pairs could include people near a peak or plateau. However, the study did not obtain a complete serial concentration curve and controlled drinking history for each person. A small difference alone cannot uniquely identify why that individual’s profile was nearly flat.

Likewise, two falling results do not, by themselves, prove that absorption and distribution were complete throughout an earlier driving interval.

How to use the evidence in a DUI review

Begin with both original laboratory reports, specimen matrices, collection times and analytical uncertainty. Calculate the observed slope transparently, keeping units consistent. Then address the additional biological assumptions needed before treating that slope as a stable elimination rate or extending it to an earlier period.

The study was retrospective, involved selected suspected impaired drivers and used historical sampling practices. Its averages do not establish a particular person’s metabolism or a present-day population error rate. No driving-performance experiment established impairment from the calculated slopes.

The site’s guide to retrograde BAC extrapolation explains the broader assumptions. This paired-sample study supplies a narrower warning: an observed short-interval decline and an individualized liver-elimination rate are not automatically the same quantity.

Primary source

Neuteboom W, Jones AW. Disappearance rate of alcohol from the blood of drunk drivers calculated from two consecutive samples: what do the results really mean? Forensic Science International. 1990;45:107–115. https://doi.org/10.1016/0379-0738(90)90227-P.