Imagine that you are driving down the highway after having a few beers at your local bar. You were celebrating at a friend’s party and having a great time. You’ve never run afoul of the law — but on this night, your reputation will change. Your blood alcohol content (BAC) is above the 0.08 limit; but you just don’t know it yet. Once the red and blue lights start flashing in your rearview mirror, you think to yourself, “How much have I had to drink tonight?”
The officer arrests you for driving under the influence of alcohol and you are taken to a station to have your blood drawn to confirm your BAC. In your mind, you’re thinking “once that blood enters the vile, I’m done for.”
But are you really “done for”? A blood test may provide some very concrete evidence for the police and prosecution, but only if the process to obtain that evidence was done properly.
For example, if the person who drew your blood wasn’t certified to perform that task, or if he or she performed the procedure in an improper fashion, then the results could be challenged.
How the blood sample is handled after it is drawn also matters greatly. Who had possession of the blood, when, and for how long, are three crucial elements to the chain of custody of a person’s blood sample. You could even call the calibration and accuracy of the device used to draw your blood into question. If there were prior problems with the equipment, or if it wasn’t properly calibrated, then the results gleaned from the blood sample could be thrown out.
Source: FindLaw, “3 Ways to Challenge a DUI Blood Test,” Maryam K. Ansari, Jan. 24, 2013