How Dallas, Texas, DWI Blood Test Results Can Be Challenged
A DWI blood result in Dallas can be attacked from several directions, and in some cases the evidence can be suppressed. The key questions are whether officers had a valid warrant, whether any consent was actually voluntary, and whether the sample was collected, preserved, and tested correctly. A laboratory number is evidence that must be examined, not a final answer, and our Dallas DWI defense team evaluates both the legality of the draw and the reliability of the testing.
If you were arrested for DWI in Dallas County, your case is handled at the Frank Crowley Courts Building. Many arrests begin with traffic stops on I-35E, I-635 (LBJ Freeway), or US-75 (Central Expressway). Blood may be drawn at the jail or at a nearby hospital and then sent for laboratory analysis, creating several points where the evidence can be challenged. Warren Abrams previously served as a Chief Prosecutor with the Dallas County District Attorney’s Office, experience that gives him direct familiarity with how the office evaluates and prosecutes these cases and informs the defense strategy he brings to clients.
Quick Facts: Challenging a Dallas Blood Test
| Question | Short answer |
|---|---|
| Can a blood result be thrown out? | Yes — through a motion to suppress under Article 38.23, Texas Code of Criminal Procedure |
| Do police need a warrant? | Usually yes. Missouri v. McNeely (2013) rejected any blanket exception for alcohol leaving the body |
| Does implied consent equal consent? | No. Reading you the statutory warning is not the same as voluntary consent (State v. Villarreal) |
| Does a draw warrant cover the lab test? | Yes — Crider v. State (2020). But blood drawn at a hospital for medical care is a different situation (State v. Martinez) |
| Where is it argued? | A pretrial hearing under Article 28.01, before trial |
| Separate deadline to watch | The license case runs on its own clock — typically 15 days to request an ALR hearing |
Did police need a warrant for your blood draw?
Usually. In Missouri v. McNeely, the U.S. Supreme Court ruled that alcohol naturally leaving the bloodstream does not, by itself, create an emergency that eliminates the warrant requirement. The analysis instead depends on the totality of the circumstances. When officers realistically had time to contact a magistrate, the need for a warrant remains.
State v. Villarreal extended that principle under Texas law. The Texas Court of Criminal Appeals held that a nonconsensual, warrantless blood draw taken under the Transportation Code’s implied-consent and mandatory-draw provisions violates the Fourth Amendment unless officers have a warrant or a recognized exception to the warrant requirement. The statute alone does not allow police to bypass a magistrate.
Was your blood drawn at a hospital instead of by police?
Blood drawn for medical care creates a different legal issue. In State v. Martinez (2019), the Texas Court of Criminal Appeals held that a person retains a privacy interest in blood drawn by a hospital for treatment. When the State later obtains those existing samples and tests them for law-enforcement purposes, that action is a search that requires a warrant or a valid exception.
This issue often appears after serious crashes on I-35E or I-635. A patient may be taken to an emergency room, have blood drawn as part of treatment, and later learn that investigators sought the hospital samples. When that sequence occurred, the way the State acquired and tested the blood becomes an important suppression question.
The rule is narrower when police obtained a valid DWI blood-draw warrant from the start. In Crider v. State (2020), the Texas Court of Criminal Appeals held that a warrant supported by probable cause for the blood draw also authorizes chemical testing of that blood. A second warrant or separate language expressly authorizing analysis is not required. Martinez therefore addresses medically drawn blood obtained later by the State; it does not create a second-warrant requirement after a valid police blood-draw warrant.
Was your consent voluntary — or just assumed?
Consent must be voluntary. Texas appellate decisions, including Burks v. State, recognize suppression issues when consent was involuntary or when officers lacked probable cause for the arrest. A judge may look closely at circumstances such as an extended detention, repeated requests, or statements that make refusal sound unavailable when deciding whether consent was freely given.
Probable cause is equally important because it comes earlier in the sequence. If the traffic stop or arrest was unlawful, evidence obtained afterward, including a blood sample, may also be subject to suppression. The observations an officer claims justified the arrest are often central to that analysis, which is why understanding what officers look for during a DWI stop can matter to the defense.
What can go wrong after the blood leaves your arm?
A legally obtained sample can still produce a result that is open to scientific challenge. The defense may examine issues such as:
- Chain-of-custody gaps — missing documentation about who possessed the sample, when it changed hands, or where it was stored
- Vial problems — insufficient sodium fluoride (the preservative), insufficient EDTA (the anticoagulant), or a compromised tamper seal that may affect the integrity of the sample
- Serum versus whole blood — hospital serum testing can produce values roughly 10 to 20 percent higher than forensic whole-blood testing
- Calibration and maintenance — incomplete, late, or missing records for the instrument used to test the sample
- Analyst issues — the qualifications of the person who performed the test and whether that analyst is available for cross-examination
- Storage and timing — the temperature at which the sample was kept and the delay between collection and analysis
How is the challenge actually made in a Dallas court?
The challenge is typically raised through a written motion to suppress under Article 38.23 and the Fourth Amendment, followed by a request for a pretrial hearing under Article 28.01. At the hearing, the officer’s testimony, the warrant, and the laboratory records can all be examined. If the blood result is suppressed, the State may be left with a significantly weaker case, which can be one path by which a DWI charge gets dismissed in Texas.
These suppression principles are not limited to one Dallas courtroom. The same constitutional rules and Texas case law apply in nearby jurisdictions, whether the case is pending in Dallas County, a Plano criminal court in Collin County, or another North Texas court.
What if your blood results have not come back yet?
Blood results can take months to arrive in North Texas, particularly in suspected drug-impaired-driving cases that require more complex testing. That waiting period should not be treated as inactive time. Video can be preserved before it is overwritten, and the administrative license case follows its own deadline, so the question of whether to request an ALR hearing needs early attention. When the alleged intoxicant is a prescription or controlled substance rather than alcohol, related drug offense issues may also need to be evaluated at the same time.
Talk to a Dallas DWI Lawyer Before Your Suppression Deadline
The best opportunity to investigate a blood draw is usually soon after the arrest, while video, records, and witness recollections are still available. If a blood result is part of your North Texas DWI case, schedule a consultation with our Dallas DWI defense team so the warrant, footage, and laboratory file can be reviewed before the prosecution builds its case around the reported number.
Frequently Asked Questions
Disclaimer: This article is provided for general informational purposes and is not legal advice. Every DWI case depends on its specific facts.