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The Role of BAC Levels in San Diego DUI Cases

By San Diego Attorney on September 3, 2025

Blood alcohol content (BAC) is one of the most important elements in any San Diego DUI case. It serves as the key metric that law enforcement and prosecutors use to determine whether a driver was legally impaired at the time of arrest.

BAC levels are more than just numbers. They influence how charges are filed, what penalties you might face, and how your defense should be constructed.

Understanding how BAC levels function within California’s DUI legal framework is essential for anyone charged with driving under the influence. This blog offers a comprehensive guide on BAC levels DUI San Diego cases rely on, exploring testing procedures, legal thresholds, the science behind BAC readings, and how experienced defense attorneys challenge their accuracy.

What is Blood Alcohol Content (BAC)?

Blood alcohol content is a scientific measurement that estimates the amount of alcohol in a person’s bloodstream. For example, a BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood.

BAC is measured through:

• Breath tests (typically done roadside using handheld breathalyzers)
• Blood tests (more accurate, usually conducted at a medical facility or police station)
• Urine tests (less common and generally used when other methods are unavailable)

Legal Limits for BAC in San Diego DUI Cases

California has established specific DUI thresholds depending on the driver’s age, license type, and other factors. Driving with a BAC above these legal limits can result in immediate license suspension and arrest, regardless of visible signs of impairment:

• 08% or higher: Legal limit for most adult drivers
• 04%: For commercial drivers
• 01%: For drivers under 21 and drivers on DUI probation

How BAC Levels Influence DUI Charges

In San Diego, BAC levels play a central role in both misdemeanor and felony DUI charges. The higher the BAC, the more severe the consequences.

Here is how different BAC levels can impact your case:

• 08%–0.14%: Standard DUI. Charged under California Vehicle Code Section 23152(b).
• 15% or higher: Considered a high BAC, triggering enhanced penalties like longer DUI education programs.
• 20% or higher: May require a nine-month DUI school, increased fines, and additional jail time.

If an accident or injury occurs and your BAC is elevated, you may face felony DUI charges with significantly harsher penalties.

BAC Testing Procedures in San Diego DUI Arrests

Once you are pulled over under suspicion of DUI, officers may perform a Preliminary Alcohol Screening (PAS) test or a field sobriety test. If arrested, you will be required to submit to a chemical test under California’s implied consent law.

• Refusing to take a test: Leads to automatic license suspension and can be used as evidence against you in court.
• Breath vs. blood tests: Breath tests are quicker and less invasive, but can be less reliable. Blood tests are more accurate but subject to strict handling and chain-of-custody requirements.

An experienced DUI attorney will scrutinize every aspect of BAC testing to look for errors, contamination, or rights violations.

Common Issues That Affect BAC Accuracy

BAC testing is not infallible. Several variables can impact the reliability of the results, including:

• Improper calibration or maintenance of breathalyzer equipment
• Contaminated blood samples
• Residual mouth alcohol (from recent drinking, mouthwash, or medical conditions)
• Incorrect administration by law enforcement
• Rising BAC levels (your BAC may have been below the legal limit while driving, but increased before testing)

These are key areas that a skilled San Diego DUI lawyer will investigate as part of your defense strategy.

Legal Defense Strategies

Effective DUI defense often hinges on undermining the credibility of BAC evidence. Here are some of the strategies that experienced attorneys use:

• Challenging the legality of the traffic stop
• Questioning the timing and method of BAC testing
• Demonstrating medical or dietary factors that may have influenced results
• Hiring forensic experts to analyze test reliability
• Filing motions to suppress improperly obtained evidence

By dissecting each stage of the arrest and testing process, a DUI attorney can often find procedural or scientific flaws that weaken the prosecution’s case.

BAC Is Not the Only Factor in DUI Cases

While BAC is central to DUI cases, it is not the sole determinant. Police observations, driving behavior, field sobriety tests, and recorded statements can also influence charges and outcomes. That is why a comprehensive defense must evaluate the entire picture, not just the BAC.

What to Do If You Are Pulled Over or Stopped at a DUI Checkpoint

Whether you are pulled over by law enforcement or stopped at a DUI checkpoint, your actions in those first few minutes can significantly impact your case.

Here is how to protect your rights and avoid unnecessary mistakes:

1. Remain Calm and Cooperative

Pull over promptly and safely. Keep your hands visible and avoid sudden movements. Cooperate respectfully with the officer’s requests for your license, registration, and proof of insurance.

2. Exercise Your Right to Remain Silent

You are not required to answer questions about whether you have been drinking, where you have been, or where you are going. Politely state that you are exercising your right to remain silent until you speak with an attorney.

3. Understand Field Sobriety and Preliminary Tests Are Optional

In most cases, you are not legally required to perform field sobriety tests or take a preliminary breath test at the roadside. These tests can be subjective and may be used to justify an arrest.

4. Be Aware of Chemical Test Obligations

If you are arrested, California’s implied consent law requires you to submit to a blood or breath test. Refusing can lead to automatic license suspension and harsher penalties—even if you are not convicted.

5. Contact a DUI Defense Attorney Immediately

If you are arrested, the best step you can take is to call an experienced San Diego DUI defense lawyer.

Finding the Right DUI Attorney

At jD Law Criminal Defense Attorneys, we combine over 30 years of criminal defense experience with insights from our lead attorney’s former law enforcement background. Our law firm knows how to analyze and challenge BAC testing protocols, uncover testing flaws, and construct robust defense strategies.

Speak With Our Experienced DUI Lawyer in San Diego Today

If you are facing DUI charges in San Diego, especially those involving elevated BAC levels, do not wait. Call jD Law Criminal Defense Attorneys at (760) 630-2000 to schedule a confidential consultation with our DUI attorney.