DWI Blood Tests and Breath Tests

Issues involving blood tests for DWI are discussed by Clarke Dummit.

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Understanding DWI Blood Tests

Are blood tests more accurate than breath tests?

Generally speaking, yes. Blood tests are actually measuring the amount of alcohol in your blood whereas breath tests are measuring keytones being blown off after your body has processed the alcohol – so much more accurate. More than that, blood tests preserve evidence so it can be retested. They typically draw at least two vials so it can be preserved for retesting. Also, procedures can be tracked and followed, whereas with breath testing, if one thing went wrong and it didn’t tell us, if the chamber wasn’t heated to the correct degree, the entire machine would give you an incorrect reading.

Can blood be improperly drawn, does that ever happen?

Absolutely. If they use an alcohol swab right before they stick a needle in, you’ve got raw alcohol going into the sample.

What about chain of custody issues?

Chain of custody is a big issue. In North Carolina, typically a trooper will be at the hospital with a blood kit, and a nurse will draw blood and hopefully follow the right procedures. However, blood is a biological material and it breaks down over time. It has to be preserved, handled, and stored properly. If it’s not, there’s no telling what could happen to the alcohol in it. It could ferment. Blood is by its very nature nondescript. If you show me two vials of blood, I can’t distinguish between which one is mine and which one is yours. It’s impossible to tell. So chain of custody is critical in these cases because every vial of blood looks the same. The North Carolina labs don’t have a real good record of keeping their records straight – we have a problem with chain of custody in this state.

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