If you’ve been arrested for driving while intoxicated (DWI) in Texas, you may have been asked — or even forced — to submit to a blood test. For many, this moment feels like the final nail in the coffin. After all, how can you fight “scientific evidence” that allegedly proves intoxication? The truth is, DWI blood test results are not always accurate, nor are they beyond challenge.
Javier Guzman is a ACS-CHAL Forensic Lawyer-Scientist — which means that he is uniquely qualified to defend you against DWI blood test evidence. He knows how lab errors, mishandled samples, and procedural mistakes can turn what seems like an ironclad case into one filled with doubt.
At Guzman Law Firm, we understand the intimidation factor that comes with blood test evidence, but we also know where to look for weaknesses in the prosecution’s case. If you’re facing DWI charges after a blood draw, you don’t have to face them alone. Call us today at (956) 516-7198 to learn how we can fight for your rights and challenge the results in court.
When, why, and how DWI blood test results are used
When a person is suspected of driving while intoxicated in Texas, police officers have several tools at their disposal. Most people are familiar with the breathalyzer, but law enforcement may also rely on blood tests in certain circumstances.
According to Texas law, you may be asked to take a blood test if:
- You refuse a breathalyzer test during a traffic stop. Under Texas’ “implied consent” laws, refusing a breath test can result in a warrant for a blood draw.
- The officer suspects drug impairment in addition to alcohol. A breathalyzer only measures alcohol concentration, not drugs.
- There is a serious accident, injury, or fatality that requires a more thorough examination.
- A judge issues a blood draw warrant, giving police the legal authority to compel the test.
What can a blood test determine that a breathalyzer cannot?
A breathalyzer measures blood alcohol concentration (BAC) indirectly by testing alcohol in a person’s breath. A blood test, however, measures the actual concentration of alcohol or drugs in the bloodstream. This can include:
- Alcohol levels at the time of testing
- The presence of prescription medications
- Illegal substances like marijuana, cocaine, or methamphetamines
- Potential drug interactions that could impair driving
Because of this, prosecutors often argue that blood tests are more scientifically reliable than breath tests.
Is it better to refuse a blood test for DWI?
Refusing a blood test in Texas is rarely the best strategy. While you technically can refuse, police officers can often obtain a warrant that forces compliance. Refusal may also lead to driver’s license suspension and can still be used as evidence of guilt.
What’s important to understand is this: agreeing to or being compelled into a blood draw doesn’t mean your case is lost. With the right defense attorney, the results can still be contested and weakened in court.
Challenging DWI blood test results
Blood test results may look scientific and definitive, but in practice, they’re vulnerable to a wide range of challenges. An experienced San Antonio DWI defense attorney will examine every aspect of the process — from how the blood was drawn to how it was stored and analyzed.
How accurate are DWI blood tests?
Blood tests are not immune to human error or technical mistakes. Even small lapses can significantly affect results. Potential issues include:
- Improper sterilization of the draw site (such as using an alcohol swab, which can contaminate the sample)
- Faulty lab equipment or calibration errors.
- Clerical mistakes such as mislabeling or mixing up samples.
- Contamination during the handling or transport of the sample.
A defense attorney may demand access to the lab’s procedures, maintenance records, and certifications. If evidence shows the lab failed to follow proper protocol, the accuracy of the test can be called into question — potentially making the results inadmissible in court.
How long does it take police to get blood test results?
It can take weeks — or even months — for law enforcement to receive finalized blood test results. During that time, the chain of custody becomes critical.
Chain of custody refers to the documented trail showing who had possession of the blood sample at each stage. If there are any gaps, inconsistencies, or unexplained delays, the defense can argue that the sample may have been tampered with, mislabeled, or mishandled.
For example, if a vial of blood sat unsealed or unrefrigerated for too long, fermentation could artificially raise alcohol concentration levels. A defense attorney will scrutinize the timeline to highlight weaknesses and argue that the results are unreliable.
How long after drinking alcohol does it show up in a blood test?
Alcohol does not instantly register in the bloodstream. In fact, it can take 30 minutes to 2 hours for alcohol to fully absorb into the blood. This means that if a blood test is administered well after the traffic stop, the results may not accurately reflect the driver’s BAC at the time of driving.
Texas is an “at the time of driving” state for BAC tests. This raises two key defense points:
- Rising BAC defense: A person may have consumed alcohol shortly before driving, and their BAC rose after they were stopped, making the results misleading.
- Improper testing timing: If police delayed the blood draw, the results may not correlate to the driver’s actual impairment on the road.
A skilled DWI lawyer can use expert witnesses to show how alcohol absorption rates vary by body type, food intake, and timing — demonstrating that the test results should not be taken at face value.
DWI blood test results are not the end of the road. Call Guzman Law Firm for defense.
Facing DWI charges with blood test evidence stacked against you can feel overwhelming. Prosecutors often lean on scientific-sounding results to make their case appear airtight. But as you’ve seen, there are numerous avenues to challenge these tests. From lab errors to chain of custody issues, from rising BAC defenses to improper procedures, blood test evidence is far from infallible.
At Guzman Law Firm, we know how to dissect the prosecution’s case and expose weaknesses in the DWI blood test results that may give you leverage in court. Every step in the testing process is an opportunity to raise doubt — and in a criminal case, doubt can be the difference between conviction and freedom.
If you or someone you know has been charged with a DWI in Laredo, San Antonio, or the surrounding areas, don’t give up hope. Call Guzman Law Firm today at (956) 516-7198 to schedule a consultation and learn how we can challenge the blood test results against you. The fight isn’t over until every detail has been examined, and we’re ready to stand by your side.
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