Challenging blood testing in drunk driving cases

Dec 07, 2010 Challenging blood testing in drunk driving cases

Image from National Institute of Standards & Technology.

Recently in a Virginia District Court drunk driving trial, the judge agreed with me not to find a blood alcohol level level higher than a 0.20 despite the 0.21 reading made by the state’s blood examination expert (“DFS analyst”). That spelled the difference between my client’s facing a five-day mandatory minimum in jail for a blood alcohol level (“BAC”) of at least 0.15 up to 0.20, and a ten-day mandatory minimum for a BAC over 0.20. Va. Code § 18.2-270.  

The prosecutor had all his witnesses present for trial, those being  the police officer, breath technician (who testified that my client’s vomiting prevented a reliable breath test), blood drawer, and DFS analyst. The defense came with forensic chemist Patrick Demers of Maine.

We were ready to argue that 10% is the generally accepted margin of error among forensic chemists for blood draws. Before trial and on the witness stand, I got the DFS analyst’s confirmation that the DFS Toxicology Procedures Manual at pp. 49-54 govern DFS blood analyses.  .

For margins of error see:

7.9.9 New calibrator certification. When new calibrators are prepared, analyze the new calibrators and recalibrate the instrument. Run the Cerilliant 0.05, 0.08, 0.10, 0.20 and 0.30% w/v controls and the Cerilliant Multicomponent Alcohol Mixtures to certify the new calibrators. The new ethanol calibrators must be within ± 6% of their target concentrations or 0.004% w/v, whichever is greater. The Cerilliant Multicomponent Alcohol Mixtures must be within ± 10% of the Cerilliant target concentration or 0.005% w/v, whichever is greater.

DFS Toxicology Procedures Manual.

Even a 6% margin of error listed in section would have brought us below a 0.20 BAC, but the DFS analyst insisted her analysis showed no margin of error in her test higher than 4%, and testified that this translated to a BAC of 0.20-0.21. Her math was off, because 0.21 minus a 4% margin of error equals 0.206.

I was were ready to argue that there is no way that the DFS expert could have reliably determined a margin of error as low as 4%. That became unnecessary after the prosecution rested, once the trial judge asked for a proffer of my expert witness’s testimony. The judge said that the prosecutor was stuck with its DFS expert’s testimony of a margin of error as low as 0.20 —- as much as the prosecutor objected to the judge’s refusal to accept the possibility of a BAC over 0.20 — and the defense rested.

Consequently, the judge convicted my client and gave him the minimum allowed by law for a 0.20 BAC, which was five days in jail, and a short suspended sentence, together with the standard mandatory conditions of one year of suspended driving (permitting restricted driving to work and a driver education program), only driving with an ignition interlock (which is required for convictions for driving with a 0.15 BAC or higher), and completion of the Virginia Alcohol Safety Action Program. .

Certainly it would have been preferable to have obtained an acquittal, or no jail time, and in many cases for the many years that I have defended drunk driving cases, I have obtained such results (past results cannot be a guarantee of future resutls, of course). On the other hand, if given a choice of a five-day sentence versus a ten-day sentence, the five-day option is preferable. Furthermore, my client’s night of arrest counted towards one day of jail credit, leaving four more jail days to serve. 

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