McKinney, Texas DWI Attorneys for Blood and Breath Tests

Lawyers Helping Clients Address Breath and Blood Tests in DWI Cases in McKinney

When a person is arrested for driving while intoxicated (DWI), multiple types of evidence may be used in their case, including chemical tests that measured alcohol in their breath or the presence of drugs in their blood. Prosecutors will often act as if breath or blood test results are conclusive evidence of intoxication, but in reality, there are multiple reasons why the results of these tests may be inaccurate. A lawyer who understands exactly how these tests work can determine whether this evidence may be challenged.

At Texas Defense Firm, we represent clients in DWI cases in McKinney and the surrounding areas, and we know what steps to take to address blood or breath tests that may be used as evidence against our clients. We can determine the defense strategies that will be most likely to be successful, and we will work to protect our clients' rights, taking steps to prevent DWI convictions whenever possible.

Breath Testing

After being arrested for DWI, a person will usually be asked to take a breath test that will measure their blood alcohol concentration (BAC). Breathalyzer devices will analyze a breath sample and provide a reading that is meant to show the level of alcohol in their system. Law enforcement officials in Texas are required to follow specific standards to ensure that breath testing machines are calibrated and maintained correctly, and the proper procedures must be followed when conducting tests.

Before a breath test is administered, an officer must observe the person for a waiting period of around 15 minutes, which is meant to rule out the possibility that residual alcohol in the person's mouth could affect the results of the test. Officers must be certified to operate breathalyzer equipment. Regular maintenance must be performed to ensure that breath testing devices are in proper working order.

Reasons Breath Test Results May Be Challenged

While breathalyzers are often treated as if they are always accurate, they have some limitations. Our attorneys can review testing procedures and records to determine whether there are any issues that may allow test results to be challenged. These may include:

• Improper Calibration or Maintenance: If a breathalyzer has not been inspected and calibrated as required, its results may not be accurate. Our lawyers can determine whether missing or incomplete maintenance records may call the results of a test into question.
• Operator Certification Issues: If an officer who administered a breath test was not properly certified, or if their certification had lapsed, the reliability of the test may be challenged.
• Failure to Observe the Waiting Period: If officers did not follow requirements for an observation period before testing, or if the waiting period was not properly documented, our attorneys may argue that mouth alcohol or other contaminants could have affected the test results.
• Interference From Other Substances: Some breath testing instruments can be affected by substances other than alcohol. Diabetes or other medical conditions could lead to falsely elevated readings, and our lawyers can highlight these issues and argue that test results did not prove intoxication.

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Blood Testing

In addition to or instead of a breath test, police officers may take steps to collect a blood sample and have it tested for the presence of alcohol or drugs. A blood draw must be performed by a qualified person, such as a doctor, a registered nurse, or a medical technician. The sample will be sent to a laboratory for analysis. Throughout the process of drawing, transporting, and testing blood, a sample must be properly preserved to prevent clotting, fermentation, or other issues that could affect the results of a test.

Chain of Custody and Other Issues That May Affect Blood Tests

Because a blood sample may pass through many hands between when it is drawn and when it is analyzed by a lab, the chain of custody of the sample must be fully documented. Our attorneys can review documentation related to the person who performed the blood draw, officers who handled the sample, and lab technicians who performed testing. Missing signatures, improper labeling, or other reasons for an unexplained gap in the chain of custody can raise questions about whether a sample may have been contaminated or switched with another sample.

Blood test results may also be affected by improper transportation and storage procedures. If a sample was not preserved correctly, fermentation could lead to inaccurate results. Errors during testing or tests performed by technicians without the proper certifications may also be reasons to challenge the accuracy of test results.

Timing may be another factor to consider when looking at the results of blood tests. Due to the period of time between when a person was driving and when their blood was drawn, the amount of alcohol or drugs in their blood at the time of testing may not reflect intoxication while they were operating a vehicle. Prosecutors may rely on estimates of a person's blood alcohol concentration when driving based on later test results. However, alcohol absorption rates can vary from person to person, and factors like food consumption and body composition may also affect a person's level of intoxication. Our lawyers can challenge assumptions related to test results and argue that they may not conclusively prove that a person was intoxicated.

The Importance of Working With a Lawyer Who Understands DWI Testing

Breath and blood test evidence plays a crucial role in many DWI cases, but there may be many opportunities to challenge this evidence. Our attorneys understand how to identify weaknesses in evidence. We know how to address the specific types of equipment used during testing, the regulations related to maintenance and operation of breathalyzer devices, and the scientific principles that apply in blood tests. We have the experience needed to protect our clients' rights and defend against DWI convictions.

Contact Our McKinney, TX DWI Testing Lawyers

Breath or blood test results will often be treated as the strongest pieces of evidence in a DWI case, but there are a variety of reasons why test results may be inaccurate. At Texas Defense Firm, our lawyers know how to address the evidence in a DWI case, and we can take steps to defend against a conviction. Contact our McKinney DWI breath and blood test attorneys at 972-369-0577 to set up a free consultation.