Can I Fight My DUI Charge With a Rising Blood Alcohol Defense?

Generally, having a high blood alcohol concentration (BAC) is bad news for a DUI defendant. In every state, it's illegal—a "per se" DUI—to drive with a BAC of .08% or more. However, there are several ways of challenging BAC test results. One of the more common ways of fighting a DUI involving a high BAC is with the "rise-blood-alcohol defense."

What Is the Rising Blood Alcohol Defense?

Defendants can sometimes use the blood alcohol defense to fight a DUI charge. This defense is about timing—specifically, the time that lapsed between the driver's alcohol consumption and the BAC measurement. When there's a short delay between these two (alcohol consumption and BAC measurement), the rising blood alcohol offense can come into play.

How Rising Blood Alcohol Can Lead to an Inaccurate BAC Reading

Everyone metabolizes alcohol at different rates. For example, the body of a smaller person would normally process alcohol more quickly than a larger person. But, regardless of body type, blood alcohol concentration is constantly changing: At any given time, BAC is either rising or falling. And there's always at least some delay between when a motorist is actually driving and BAC testing occurs.

Because of this delay, we know that a driver's BAC changes between the time of driving and the time of the BAC measurement. In other words, the BAC measurement can't tell us exactly what the driver's BAC was at the time of the actual driving.

Using the Rising Blood Alcohol Argument to Beat a DUI Charge

The rising blood alcohol defense is premised on the driver's BAC being on the upswing between the time of driving and BAC testing. During the upswing, the body is absorbing the consumed alcohol and BAC is rising. So, the argument is that the driver's BAC was below the legal limit while driving but rose above the limit during the delay between when the driver was stopped by police and testing occurred.

Does the Rising Blood Alcohol Argument Work in Every State?

The rising blood alcohol defense doesn't work in all states. In response to defendants using the rising blood alcohol defense, some states—including Nevada, Colorado, and Kentucky—changed their DUI laws.

State DUI Laws that Eliminated the Rising Blood Alcohol Defense

Some states have largely eliminated the rising BAC defense by defining a per se DUI as having a BAC of .08% or more within a certain time (typically, two or three hours) of driving. By defining a per se DUI in this way, these states have essentially made the time delay between driving and testing irrelevant, so long as the testing occurs within the statutory time window of two or three hours.

For drivers in these states, the traditional rising BAC defense generally isn't an option.

When BAC Testing Occurs Outside the Two- or Three-Hour Window

In the vast majority of cases, police can complete BAC testing within the statutory time window. However, if for some reason police can't make this happen, the driver might have a viable defense, at least against a per se DUI charge. The driver still isn't exactly in the clear, but this scenario can alleviate some of the pressure from the prosecution.

Proving the Rising Blood Alcohol Defense in a DUI Case

Normally, establishing the rising-blood-alcohol defense requires testimony from an expert. In other words, the science of how alcohol metabolism works needs to be explained to the jury by a witness who's knowledgeable about the process. This can sometimes be accomplished through cross-examination of a prosecution witness. But oftentimes, the defense will call their own expert to testify on the subject.