There are lots of ways to fight a DUI charge. The defenses that will give you the best chance of beating a DUI charge depend on the laws of your state and the specific circumstances of your case. But one of the most common defenses to a DUI charge is called the "rising blood alcohol" defense. This defense relies on how the body processes ingested alcohol and how this process affects blood alcohol concentration (BAC).
This article discusses how prosecutors and defense attorneys use the phenomena of rising and falling BAC in DUI cases. In other words, BAC fluctuation may come into play when the prosecution is trying to prove a DUI charge and the defense is trying to avoid a conviction.
Why a Driver's BAC (Blood Alcohol Concentration) Is Important in a DUI Case
After arresting a driver on suspicion of DUI, police typically measure BAC using a breath, blood, or urine test. (The law presumes that drivers have consented to DUI testing.) Drivers with BACs that are over the legal limit—.08% or higher is illegal for drivers who are at least 21 years old (.05% or more in Utah)—can be convicted of a per se DUI.
In a per se DUI prosecution, the focus is on the driver’s BAC—not whether the driver’s ability to drive safely was actually impaired. To get a conviction, the prosecution needs to prove the driver's BAC was over the limit during the relevant time period. Whether the prosecution can successfully prove BAC can mean the difference between a conviction and an acquittal.
(Be aware that all states also have laws against driving while impaired, sometimes called “impairment DUI” or “DUI-less-safe.” These laws apply even where there’s no chemical test showing BAC.)
Your BAC Level Is Constantly Changing After You Drink Alcohol
After you drink alcohol, your body begins to process it. Your blood alcohol concentration rises as the alcohol is absorbed into your body, then falls as the alcohol dissipates or burns off. In other words, after drinking alcohol, your BAC is always in a state of rising or falling until all the alcohol is out of your system.
How the Rising BAC Defense Works
In states where the prosecution has to prove your BAC was over the limit at the time of driving, defense attorneys often use a “rising BAC” defense at trial. The theory of this defense is that you were under the legal limit when you drove, but, because the alcohol was still being absorbed into your system, your BAC rose to an illegal level by the time you were tested.
To establish this defense, an attorney might bring in an expert witness who can look at your measured BAC and “extrapolate” what your approximate BAC was at the time of driving. An expert testifying that your BAC was likely below the legal limit while you were driving could improve your chances of beating the charge.
Factors That Can Affect the Rising Blood Alcohol Defense
Everyone metabolizes alcohol at different rates. For example, women typically absorb alcohol more quickly than men, and alcohol ordinarily leaves a larger person’s body at a faster rate than it would for someone smaller. Experts often rely on these factors—gender and body size—and a number of other circumstances to extrapolate a driver’s BAC. These other circumstances might include:
- the number and type of drinks the driver had
- how the driver consumed the drinks (shots or sips)
- when and what the driver last ate
- the passage of time (between consumption and driving, consumption and testing, and driving and testing), and
- any medical conditions the driver had that affect liver function.
By looking at factors like these in combination with known average absorption and dissipation rates, an expert can estimate the driver’s BAC at the time of driving.
How Prosecutors Counter the Rising BAC Defense
If, when tested, your BAC was below but near the legal limit, the prosecutor might argue to the jury that your BAC was actually higher when you drove but it had fallen by the time you were tested. (The falling blood alcohol phenomenon is sometimes called alcohol “elimination.”)
An expert witness for the prosecution might use some of the factors mentioned above to extrapolate that your BAC at the time of driving was higher than when it was measured by police. The jury could find you guilty of a per se DUI even though your BAC was below the legal limit when you were tested.
Talk to a DUI Attorney in Your Area
The consequences of a DUI conviction are serious, and the circumstances of each case are unique. If you've been arrested for driving under the influence, you should get in contact with a knowledgeable DUI attorney in your area. A qualified DUI lawyer can tell you how the law applies to the facts of your case and advise you on viable defenses.