Understanding Blood Warrants in Texas DWI Cases
In Texas, when a driver is suspected of Driving While Intoxicated (DWI), law enforcement may request a blood or breath sample to measure blood alcohol concentration (BAC). If the driver refuses to provide a sample voluntarily, officers may seek a blood warrant to obtain that evidence by force, with court approval.
This post explains the legal process, requirements, and limits of blood warrants in DWI investigations under Texas law.
What Is a Blood Warrant?
A blood warrant is a court order authorizing law enforcement to draw a person’s blood for chemical testing, usually to detect alcohol or drugs. It is typically used in DWI cases when:
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The suspect refuses to voluntarily provide a breath or blood sample, and
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Police believe there is probable cause to show intoxication
The warrant allows medical personnel to collect a blood sample, even over the suspect’s objection.
When Can Police Get a Blood Warrant?
Under Texas Transportation Code § 724.012 and Chapter 18 of the Texas Code of Criminal Procedure, officers may apply for a blood warrant in a DWI investigation when:
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There is probable cause to believe the person was driving while intoxicated, and
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The suspect refuses testing, and
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A magistrate or judge approves the warrant after reviewing a sworn affidavit.
Probable cause may come from:
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Driving behavior (e.g., swerving or reckless driving)
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Smell of alcohol or drugs
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Slurred speech or poor coordination
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Field sobriety test performance
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Witness reports or accident evidence
Mandatory Blood Draw Situations (Without a Warrant)
In the past, Texas law allowed mandatory blood draws without a warrant under certain conditions (e.g., serious injury crashes, prior convictions). However, in 2014, the U.S. Supreme Court ruled in Missouri v. McNeely, 569 U.S. 141 (2013), that a warrant is generally required unless exigent circumstances exist.
As a result, most forced blood draws in Texas now require a judge-signed warrant.
How Are Blood Warrants Obtained?
Police obtain blood warrants using a process that often includes:
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Drafting an affidavit laying out probable cause
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Submitting the affidavit electronically to an on-call judge or magistrate (often via email or e-warrant system)
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Judge reviews and signs electronically
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Officers transport the suspect to a hospital or clinic, where licensed personnel draw the blood
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The sample is sent to a lab for analysis, which may take weeks
In Smith County and other parts of East Texas, many law enforcement agencies use electronic warrant systems, which allow blood warrants to be issued 24/7, including weekends and holidays.
Can a Blood Draw Be Contested?
Yes. While a blood warrant is a powerful tool for prosecutors, it must follow strict legal protocols. Defense attorneys often challenge:
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Whether probable cause existed
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Whether the affidavit was sufficient
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Whether the blood draw was performed properly
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Whether the sample was handled and preserved correctly
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Whether the delay in testing affected the BAC level
Improperly obtained or executed warrants can result in evidence being suppressed, which may impact the prosecution’s case.
Legal Rights of the Accused
Even if a blood warrant is issued, individuals still have constitutional protections under the Fourth Amendment against unlawful search and seizure. These protections include:
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The right to contest the warrant’s validity
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The right to be informed of the reason for arrest and the testing
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The right to challenge the admissibility of blood test results in court
Summary
In Texas DWI cases, blood warrants are used to obtain BAC evidence when a suspect refuses voluntary testing. While these warrants are routine in many jurisdictions, they must comply with constitutional requirements and proper procedure.
Blood evidence can be a powerful tool in court, but it is not immune to legal scrutiny. Understanding how blood warrants work is essential for anyone involved in the DWI legal process—whether as a defendant, criminal defense attorney, or concerned citizen.
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