The Role of Blood Alcohol Content (BAC) in DUI Defense Cases

Posted: April 15, 2024 at 12:00 am
Driving under the influence (DUI), also known as driving while intoxicated (DWI), is a serious offense with potentially life-altering consequences. A key piece of evidence law enforcement uses to determine impairment in DUI cases is Blood Alcohol Content (BAC). Let’s consider the role of BAC in DUI defense strategies as explained by a DUI defense lawyer serving Lenexa, KS, and Shawnee, KS.

The Role of Blood Alcohol Content (BAC) in DUI Defense Cases: Thoughts From a DUI Defense Lawyer in Lenexa, KS and Shawnee, KS

Legal Limits for Blood Alcohol Content (BAC) in Kansas

Blood alcohol content (BAC) is the percentage of alcohol present within your bloodstream. A BAC of 0.10%, for example, means there is 0.10 grams of alcohol for every 100 milliliters of blood. 
Someone with a BAC below 0.05% is generally considered not impaired. A BAC of 0.05% to 0.07% means the person is possibly impaired, though it is not conclusive. A person with a BAC of 0.08% or higher is legally considered intoxicated in the state of Kansas. Kansas has very strict laws for underage drinking and driving. A minor can be charged with a DUI even if their BAC is only 0.02%: far lower than the adult limit. If their BAC is 0.08% or higher, they’ll be charged with a full adult DUI.

Kansas prosecutors rely heavily on BAC readings as evidence of a DUI offense. A BAC above the legal limit simplifies their case, suggesting the driver was automatically impaired. However, a DUI conviction doesn’t depend just on a BAC test result, and a skilled DUI attorney will analyze both the BAC levels and additional factors to build the strongest possible defense strategy.

How BAC Is Usually Measured


This is the most common method used in the field. It’s based on the principle that alcohol in your bloodstream is in equilibrium with alcohol in your breath. The device estimates your BAC from your breath alcohol levels. While convenient, breathalyzers can be less accurate than blood tests.

Other Tests

Blood tests are the most accurate for determining BAC, and while urine tests are also sometimes used for BAC, they are less common and less accurate than blood tests. Neither, however, is commonly used by law enforcement due to the challenges of collecting samples in the field. They are therefore not always a factor in DUI defense cases.

Defending Against BAC Evidence

Challenging the BAC Test’s Accuracy

It is possible for breathalyzer and even blood test results to be inaccurate. Improper calibration of the machines, administration errors, or even certain medical conditions can affect the readings.

Time of Consumption

The BAC level at the time of arrest may not reflect the driver’s BAC level at the time of driving. Alcohol absorption and elimination rates vary depending on factors like weight, food consumption, and metabolism.

Rising BAC Phenomenon

In some cases, a person’s BAC can continue to rise even after they’ve stopped drinking. This “rising BAC” phenomenon can lead to an inaccurate BAC reading if the test is administered too soon after consumption.

Other Defense Considerations

Field Sobriety Test Performance

A BAC test result is not the sole determining factor in a DUI conviction. Another factor often brought up by a skilled DUI attorney is law enforcement’s use of field sobriety tests (FSTs), like the walk-and-turn test or the one-leg stand, to assess a driver’s coordination and balance. However, these tests are subjective and open to interpretation. Factors like age, medical conditions, or even uneven surfaces can impact performance.

Driving Behavior

Traffic violations like reckless driving, swerving, or speeding can support DUI suspicions. However, an attorney will examine all circumstances around the driving behavior. They can explore factors like fatigue, driver distraction, or adverse weather conditions to offer alternate explanations for any driving anomalies.

Circumstances of the Traffic Stop

An unlawful traffic stop is powerful grounds to challenge DUI charges. A DUI defense attorney will thoroughly review the initial reason for the traffic stop to ensure the officer had a valid basis for initiating contact. Any lack of probable cause for the stop could potentially lead to evidence becoming inadmissible.

Miranda Rights Violations

You have the right to remain silent and the right to an attorney. Law enforcement must inform you of these Miranda rights before custodial interrogation. Statements made in violation of your rights may be inadmissible in court, so an attorney will take a careful look at the arrest procedure to identify if there were any violations of your rights.

The Importance of Skilled Legal Representation

An experienced DUI lawyer has an n-depth knowledge of specific Kansas DUI laws and how they apply to your case. They can identify potential defenses that you may not be aware of, and even spot changes in the law that could benefit your case.

Challenging Evidence

Police and prosecutors rely heavily on BAC tests and field sobriety tests, but a skilled attorney will explain the scientific principles related to these tests, and, based on that understanding, analyze the collection, testing, and interpretation of this evidence. They will work to uncover any inconsistencies or flaws that could be used to your advantage.

Protecting Your Rights

From the moment of your arrest, your constitutional rights are at stake. An attorney ensures that law enforcement procedures were strictly followed, that your Miranda rights were upheld, and any illegally obtained evidence is suppressed. They’ll keep an eye out for any infringements of your rights.

Getting You Through the Court System

Your attorney’s knowledge of the right language and procedures will help you navigate the court system smoothly. They will handle all court appearances, legal filings, and negotiations with the prosecution on your behalf.

Negotiating for a Favorable Outcome

An experienced DUI lawyer can advocate for you to potentially reduce charges, minimize penalties, or negotiate alternative plea deals that protect your driving record and your future. They may have existing relationships with judges and prosecutors, which can smooth negotiations and increase the likelihood of a positive outcome.

Avoiding Long-Term Consequences

The consequences of a DUI conviction can affect the rest of your life, ranging from steep fines to license suspension or even jail time, not to mention higher insurance premiums and a criminal record that may affect employment and other opportunities. An attorney fights hard to minimize these consequences and protect your future. They understand the long-reaching impact of a DUI conviction, and that motivation drives them to fight for the best possible outcome.

While you have the right to represent yourself, the consequences of a DUI conviction are so severe that having a skilled DUI lawyer on your side significantly increases your chances of a successful outcome. 

The Importance of Acting Quickly

If you’ve been charged with a DUI, time is of the essence. Evidence in DUI cases can become irretrievable over time and delays can weaken your defense options. Look into legal representation as soon as possible for help with evaluating your case and explaining your rights, so you can begin strategizing your defense immediately. Your future may depend on having the right defense team by your side.
Don’t gamble with your future. Contact Henderson Legal Defense, LLC today for a consultation, and let us advocate for you.