Challenging a DWI Blood Test in Texas
A blood test result is a number on a piece of paper produced by people using equipment, and every step between your arm and that paper can be examined. A blood result is evidence. It is not a verdict, and it is not the end of your case.
Most people assume a blood number ends the conversation. Prosecutors count on that assumption. It is wrong often enough that blood cases are among the most winnable DWI cases there are — but only if someone actually requests the underlying records and reads them.
The search warrant affidavit
If you refused testing, an officer applied for a warrant to draw your blood. That application is a sworn affidavit that had to establish probable cause for a magistrate, and it is a document written quickly, often in the middle of the night, sometimes from a template.
We read it against the video. Where the affidavit describes indicators that the bodycam does not show, where it omits facts the officer knew, or where it contains statements made knowingly or with reckless disregard for the truth, that is challengeable at a hearing. On no-refusal weekends, when an on-call magistrate is signing warrants as fast as they arrive, this scrutiny matters most.
The draw itself
Texas law governs who may draw blood and under what conditions. We examine who performed the draw and their qualifications, whether the site was prepared with a non-alcohol antiseptic, whether the correct tube containing anticoagulant and preservative was used, whether the tube was expired, whether it was properly inverted, and how the sample was stored and transported. A vial that sat in a hot patrol car has a chemistry problem, and that problem shows up in the number.
The laboratory
We request the full analytical package, not the one-page report the State hands over: the chromatograms, the calibration and maintenance records, the quality control runs, the analyst's training file, and the accreditation records for the lab. Errors in this material are not exotic. They are ordinary, and they are only found by people who ask for the file.
Your BAC at the draw is not your BAC while driving
Blood is usually drawn one to three hours after the stop. Alcohol absorption and elimination are not instantaneous, which means the number in the report describes a moment that was not the moment you were driving. When the State reaches backward from the lab result to the time of driving, it is doing retrograde extrapolation, and that calculation depends on assumptions about your drinking timeline, food intake and metabolism that the State frequently cannot support.