Can a breath test and a blood test from the same DUI subject have different results?
A new academic paper examines whether or not the same subjects, who should have the same alcohol factors when being tested, could have different results when blood is drawn from them, and when a breath machine tests their blood at the same time. In Orange County DUI cases, both DUI blood tests and DUI breath tests, are used to measure alcohol.
Published on November 20, 2015, the paper, titled “Comparison of venous blood alcohol concentrations and breath alcohol concentrations measured with Draeger Alcotest 9510 DE Evidential” was published in the Forensic Science International Journal.
Noting that most blood and breath comparisons over the past 70 years were done as either drinking trials, or using police report data, which often had discrepancies and variance in timing between the breath machine test and the extraction of blood, the study set out to test blood under realistic circumstances and using strict protocols to ensure valid measurements.
Using 78 people for the test, in Germany, the test researchers used very short timing protocols, to ensure that the breath and blood were drawn from the body fairly close to one another.
It was shown in the paper that the ratio of blood alcohol to breath alcohol had a wide discrepancy. As measured in the group, it varied greatly (between 1571:1 and 2394:1) and the ratio was shown to increase with increasing BAC. A constant conversion factor that is suitable for variable forensic purposes could not be presented.
Can a breath test and a blood test from the same DUI subject have different results? Yes.
And that means problems for trying to correlate DUI cases between a breath test, and a blood test, which in the real world of DUI arrests are not taken together, almost ever. Especially with high blood alcohol DUI cases, this might be a problem. If there is a discrepancy between results, that might mean that the DUI blood testing was not accurate, or the DUI breath testing was not accurate, both, or that the actual measurement discrepancy is variable for reasons discussed in the paper.
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