Blood Alcohol Testing for DUI

How police use blood tests to determine blood alcohol concentration (BAC) in drunk driving investigations, and how the defense can challenge the results in court.

All states' implied consent laws require drivers who are lawfully arrested for driving under the influence (DUI) to consent to a chemical test. Chemical test results are frequently used by prosecutors to prove a DUI charge in court. The test will most likely be a breath or blood test. Here are some of the tactics defense attorneys use to call blood test results into question.

Challenging Blood Test Results in Court

Generally, defense tactics for challenging blood test results in court fall into two categories: challenging test result reliability and arguing the blood sample was obtained illegally.

Reliability of Blood Tests

Blood tests are more reliable than breath tests in general, but they are not without flaws. Blood samples must be handled and stored precisely. Otherwise, the blood sample may become contaminated and no longer provide an accurate measurement of the suspect's BAC level. For example, a laboratory's carelessness could theoretically result in a blood sample fermenting in the vial. Because the test matters, or the results from the test count.

The alcohol content of the blood sample rises due to fermentation. If fermentation occurs, there is no way to tell how much alcohol came from what the suspect drank and how much came from fermentation. Another shortcoming of blood testing is the time lag between when the suspect was driving and when the blood test is performed. A person's blood alcohol level is constantly changing, and it takes time for alcohol to enter and exit the bloodstream. If a defendant drank just before getting behind the wheel, the alcohol could still be in the defendant's bloodstream at the time of the arrest.

The defendant's BAC will continue to rise as the alcohol is absorbed. As a result, the defendant's blood alcohol content (BAC) will have been lower than he was driving. It may be an hour or so later when the blood draw is performed. This is known as the "rising-blood-alcohol" defense. The basic argument is that, while the BAC was higher than the legal limit at the time of the blood draw, it was lower when the defendant was driving. (Some states, such as Colorado and Nevada, have defined driving under the influence in such a way that this defense is no longer applicable.)

Unlawful Search and Seizure

The Fourth Amendment to the Constitution of certain states has protects citizens from unreasonable searches and seizures. In general, a warrantless search and seizure is considered "unreasonable" and violates the constitution.

The Supreme Court has ruled that blood draws fall under the Fourth Amendment's search-and-seizure protections, and that police typically require a warrant or the suspect's consent to lawfully draw blood. However, in certain circumstances, such as when the suspect is unconscious, police are excused from obtaining a warrant before ordering a blood draw.

As a result, in many cases where police require the suspect to submit to a blood test without first obtaining a warrant, the defense attempts to have the blood test results thrown out as the result of an illegal search and seizure. If the defense is successful, the blood test results cannot be used by the prosecution in court, and the charges are likely to be dropped.

Seek the Assistance of an Expert DUI Attorney

DUI law is difficult to understand, especially when it comes to chemical testing. If you've been arrested for DUI, you should contact a DUI Defense Attorney in Shorewood, IL right away. An experienced DUI attorney can assess your case and advise you on whether you have any viable defenses to the charges.