Is the blood test more accurate than the breath test?


Mr. Taylor (retired) describes how the blood test from a DUI suspect is sometimes mishandled and how DUI attorneys like Mr. Taylor often challenge the results of this test. Mr. Taylor’s firm has its own forensic toxicologist who re-analyzes the blood to confirm the results of the blood test. Several things can lead to a contaminated blood test, such as when the blood is not properly preserved by the authorities, which in turn causes the blood alcohol level of the blood to rise to a level that is inaccurate. The most common way a blood test can be mishandled is through the “chain of custody”. By the time the blood goes from the police officer to the arrestee’s attorney for re-testing, it can be easily mixed up with another person’s blood test. Mr. Taylor’s firm had one such case, where it was determined through a DNA test that the blood was not Mr. Taylor’s clients, which not only resulted in the criminal charges being dropped, but also a front-page editorial in the Los Angeles Times.

Show Transcript


Potentially, the blood test is more accurate. I say potentially because there are a number of things that can go wrong, and do go wrong, routinely in a blood test, and that’s why we have our own forensic toxicologist re-analyze the blood from their crime lab, just to confirm or not the blood test. One of the things that can go wrong, for example, is fermentation. If blood sits in a vial for an extended period of time without sufficient sodium fluoride or other preservative and without being refrigerated, then by the time it gets to the lab it will begin to deteriorate and produce alcohol within the blood. It’s an organic substance and when fermentation takes place, alcohol is produced. A second is coagulation. Again, if the blood is sitting in vial without anti-coagulant than the blood clots, it coagulates and as it does, solids form, leaving less liquid. It’s the liquid part of the blood, the plasma, that is going to be analyzed. With less liquid, the amount of alcohol proportionately increases and you’re going to have a higher blood alcohol concentration. Finally, and I shouldn’t say finally, in that these are the only but the most common, is the chain of custody and that is, they’ve got to prove that the blood they tested came from your client and that’s not to be taken for granted. These things can be misplaced, mislabeled, in the, perhaps, week between the time the police officer gets the blood, goes to the evidence locker, it’s transported, goes to the crime lab, it’s put in a batch of perhaps forty vials, given numbers and tested, they can get mixed up. We have had a number of cases where we were convinced that the blood was not our clients. We’ve done blood types; in one case, even though the blood type came back identical, it was an “O” very common. So we ran a DNA test; it took about three months and quite a bit of money, but it proved that our client was not the person who produced that blood and not only were the criminal charges dismissed, but the Los Angeles Times featured it on the front page of their metropolitan edition.

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