Rising Blood Alcohol: How It Can Be Used as a DUI Defense in California

A breath or blood test showing a driver was over the legal limit does not necessarily establish that the driver was over the limit when they were actually driving. In some California DUI cases, a person’s blood alcohol concentration (BAC) may still have been increasing after the traffic stop.

This concept is commonly known as the rising blood alcohol defense. Depending on when a person consumed alcohol, when they drove, and when the chemical test occurred, a later test may show a higher BAC than the person had while behind the wheel.

For someone arrested for DUI in Chico, Butte County, or elsewhere in Northern California, the timing of alcohol consumption and chemical testing can therefore become an important part of the defense.

What Is Rising Blood Alcohol?

After a person drinks alcohol, it takes time for that alcohol to be absorbed into the bloodstream. Alcohol does not necessarily cause an immediate peak in BAC.

As alcohol is absorbed, a person's BAC generally rises until reaching a peak. It then begins to fall as the body eliminates alcohol.

This creates an important question in a California DUI case:

Was the driver's BAC still rising when the breath or blood test was administered?

If the answer is yes, the test result may overstate the driver's BAC at the time of driving.

For example, suppose a driver consumes alcohol shortly before leaving a restaurant. The driver is stopped shortly afterward but does not provide a chemical sample until substantially later. If the driver's BAC was still increasing during that period, a test result of .08% or above does not necessarily mean the driver's BAC had already reached that level while driving.

Why Timing Matters in a California DUI Case

California DUI prosecutions commonly involve two separate theories. A person may be prosecuted for driving while under the influence and for driving with a BAC of .08% or greater.

The timing of the chemical test is important because the prosecution ultimately must connect the evidence obtained after the traffic stop to the defendant's condition while driving.

A DUI investigation might involve several different times, including:

• When the driver had his or her last drink

• When the driver finished drinking

• When the driver began driving

• When the traffic stop occurred

• How long the roadside investigation lasted

• When a preliminary breath test was administered

• When an evidentiary breath or blood sample was obtained

A Northern California DUI defense attorney may carefully reconstruct this timeline when evaluating whether rising blood alcohol could be an issue.

A .08% Test Does Not Always Mean a .08% BAC at the Time of Driving

Consider a driver who finishes drinking shortly before getting into a vehicle. Police stop the driver 15 minutes later. After field sobriety tests, questioning, arrest, transportation, and chemical testing, the driver's blood is drawn considerably later.

Assume the eventual test reports a BAC of .09%.

The prosecution may argue that this result establishes the driver's BAC while driving. But that conclusion may depend on assumptions about alcohol absorption and elimination.

If the driver's BAC was .07% while driving and continued increasing before reaching .09% at the time of testing, the later result does not necessarily establish that the driver drove with a BAC of .08% or greater.

The closer a chemical result is to the legal threshold, the more significant these timing questions may become.

Retrograde Extrapolation and DUI Cases

Prosecutors may use expert testimony to estimate a person's BAC at an earlier time. This process is sometimes called retrograde extrapolation.

An expert may take a later chemical test result and attempt to calculate what the driver's BAC was at the time of driving. But such calculations can depend on assumptions about factors such as the person's drinking pattern, absorption, elimination, and whether the person had reached peak BAC.

If the person was still absorbing alcohol, simply calculating backward from a later result may not accurately reflect the driver's BAC while driving.

Defense attorneys can examine the assumptions underlying these calculations and determine whether they are supported by the actual evidence.

Evidence That May Support a Rising Blood Alcohol Defense

Whether this defense applies depends heavily on the facts of the particular case. Relevant evidence can include receipts, surveillance footage, witness statements, body-worn camera footage, the police report, dispatch records, breath-testing records, blood-draw times, and the defendant's statements about when and how much alcohol was consumed.

The defense may also consult a toxicologist or other qualified expert to evaluate whether the chemical test result is consistent with a BAC that was below the legal limit at the time of driving.

This is one reason an attorney should look beyond the number printed on a laboratory report. The timeline behind the number may be just as important as the number itself.

Rising Blood Alcohol May Also Affect Allegations of Impairment

The significance of rising BAC is not necessarily limited to whether a driver exceeded .08%.

If a driver's BAC was lower during the period of actual driving, that information may also be considered alongside other evidence of alleged impairment. This can include driving behavior, performance on field sobriety tests, speech, balance, coordination, statements made to officers, and observations captured on body-worn camera.

A DUI case should therefore be evaluated based on the entire body of evidence rather than the chemical test result alone.

How a Northern California DUI Attorney Can Challenge the Prosecution's BAC Evidence

A DUI defense attorney may investigate whether the prosecution can reliably establish the defendant's BAC at the relevant time. This can involve reviewing the drinking timeline, identifying delays between driving and testing, examining laboratory records, challenging assumptions made by prosecution experts, and consulting an independent toxicologist when appropriate.

Other issues may also affect the reliability or admissibility of chemical evidence, including testing procedures, equipment maintenance, sample collection, contamination, fermentation, and compliance with applicable regulations.

The appropriate defense depends on the evidence in each case.

Charged With DUI in Chico or Northern California?

A BAC result should not automatically be treated as the end of the analysis. When alcohol was consumed shortly before driving or when significant time passed before chemical testing, rising blood alcohol may be an important issue to investigate.

An experienced Northern California DUI defense attorney can review the timeline, police reports, body-worn camera footage, chemical testing records, and other evidence to determine whether the prosecution can prove the driver's BAC at the time of driving.

If you have been arrested for DUI in Chico, Butte County, Glenn County, Tehama County, Yuba County, Sutter County, Colusa County or elsewhere in Northern California, consider speaking with a criminal defense attorney about the evidence and defenses that may apply to your case.

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