Chemical Testing

Chemical Testing in DUI Cases: Understanding the Process and Defenses

Chemical testing is central to DUI cases in California.  A DUI case often involves blood or breath testing to determine a driver's blood alcohol content (BAC). Many assume that a high BAC result guarantees a conviction, but there are numerous ways to challenge these tests. An experienced DUI defense attorney can effectively question the validity of chemical test results and use proven strategies to defend against DUI charges.

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PAS test vs. Evidentiary Test:  It is important to understand the types of chemical tests you may be asked to perform.  During the pre-arrest part of your case, the officer is investigating you for driving under the influence of alcohol, and may ask you to blow into a Preliminary Alcohol Screening Device.  This is considered a Field Sobriety Test, so it is voluntary, and generally the results of this test are not recorded, and are usually not admissible in court.  Some agencies require the officer to tell you that it is a voluntary test, and you can feel free to decline the test.

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After you are arrested on suspicion of driving under the influence of alcohol, you are supposed to be advised of your obligation as a licensed driver to submit to an evidentiary chemical test.  The officer is supposed to advise you of this obligation and to warn you that if you refuse to take an evidentiary chemical test, then your driving privilege will be revoked for a year or longer.  You will have the option of providing a breath sample or a blood sample.  If you choose to take a breath test, after the test, the officer should advise you that the breath machine does not keep a sample of your breath for re-testing, so if you want a sample collected that you may ask an independent lab to test, you will need to submit to a blood test.  

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Finally, if you refuse to take a chemical test, the arresting officer may ask a judge to issue a warrant to obtain your blood.  Some agencies will even authorize the officers to restrain you in order to obtain the blood to be tested.  If the officer does obtain a warrant, that does not erase the refusal and possible consequences from that decision. 

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Types of Chemical Tests

• Breath Tests: Commonly used for alcohol-related DUIs, breath tests measure BAC by analyzing breath samples. While convenient, they can be inaccurate due to factors like residual mouth alcohol, improper calibration, or officer error.  The officer is supposed to obtain two test results that are within 0.02 of each other to be valid, and generally the tests should be separated by about 2 minutes from each other.
• Blood Tests: Considered more accurate than breath tests, blood tests directly measure alcohol in the bloodstream. However, errors in sample collection, storage, or analysis can lead to unreliable results.
• Urine Tests: Some agencies will allow urine testing in some drug cases, but generally they are no longer an option.

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Legal and Technical Defenses

One of the most important aspects of a DUI case is the timing of the chemical test. A person's BAC can rise after they stop drinking, meaning their BAC at the time of testing might not accurately reflect their level at the time of driving. This discrepancy can form the basis of a strong defense.

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Breath tests, for example, can produce inaccurate results due to mouth alcohol from recent drinks, medications, or dental work. Additionally, errors in machine calibration or officer training can compromise the results. Blood tests, while more reliable, are not immune to errors either, such as improper sample handling, storage, inadequate preservative, or contamination.

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Chemical Test Refusals

In California, refusing a chemical test after a lawful DUI arrest can lead to additional penalties, including a one-year (or longer) driver's license suspension. However, officers are required to inform individuals of the consequences of refusing the test, and failure to do so may provide grounds for defense.

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Fighting BAC Results

Even if a chemical test shows a BAC over the legal limit, that doesn't mean the case is lost. A skilled DUI defense attorney can challenge the reliability of the tests, the qualifications of those administering them, and the methods used to collect and analyze the samples. Additionally, factors like medical conditions (e.g., GERD) can skew test results and may be used to create reasonable doubt.