How Chemical Tests Work in DUI Cases


You may be wondering how a chemical test of your blood, breath, or urine affects your DUI case.

In most situations, chemical testing is conducted for forensic purposes — meaning it is designed to create scientific evidence that the prosecutor can use in court. Typically, the State relies on a breath or blood test to try to establish your blood alcohol concentration (BAC) and support what’s known as a DUI per se charge.

A breath test is usually administered at the police station by an officer who is certified to operate the testing device. The result generated by that machine is what the prosecution will attempt to use to show that your BAC was at or above the legal limit of 0.08%.

A blood test follows a different process. The sample is drawn by a nurse, phlebotomist, or other qualified medical professional. It is then sent to the Georgia Bureau of Investigation’s Division of Forensic Science, where a forensic toxicologist analyzes the sample. After testing, a formal report is prepared and provided to the prosecutor, stating the alleged blood alcohol concentration.

If that reported number is at or above the legal limit, the State will use it in an effort to prove a DUI per se violation. That makes the accuracy of the testing procedure, the handling of the sample, the qualifications of those involved, and the scientific reliability of the results critically important. In appropriate cases, those issues can be challenged in court to determine whether the evidence should be admitted at all.

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