When a person is arrested in Arizona for driving under the influence (DUI), and a blood sample is drawn, the arresting officer is required to advise the person that they may have an independent test of their blood performed. However, in Arizona it is very difficult to find a facility willing to draw blood after business hours (typically when a DUI arrest occurs), and test it for alcohol concentration. By the time the person finds such a facility, secures transportation to that facility, and waits for blood to be drawn, many hours have passed. Due to the fact that alcohol disappears from one's system over time, this is can be an important issue.
Furthermore, the trauma of being arrested for a DUI often makes individuals not inclined to embark on a journey to retest their blood right after being released from police custody. Most people are so upset by what can be a multi-hour ordeal, when they leave the police station they ask the cab driver or friend to take them right home. What these people don't realize is that the state's lab test of their blood alcohol concentration (BAC) is not always 100% correct. Some even think that the state's crime lab will clear them of wrongdoing. That is until they see the results.
Additionally, most people don't know that during a typical trial in a DUI case, Arizona city and county prosecutors love to tell the jury that the defendant had an opportunity to get an independent blood test done, yet chose not to have his or her blood retested. This statement implies to the jury that the defendant was guilty, and knew that fact-regardless of whether that is true or false.