Many people believe that blood test evidence is impossible to challenge in a Texas DWI case. Because blood testing is often viewed as the “gold standard” of chemical evidence, drivers may assume there is little hope once a laboratory reports a blood alcohol concentration above the legal limit. In reality, blood testing is a complicated scientific process involving multiple people, procedures, and pieces of equipment. Mistakes can happen at every stage, and those mistakes may create important defenses.

If you were arrested for DWI in Longview or elsewhere in East Texas, an experienced DWI defense attorney may carefully investigate how your blood sample was collected, handled, transported, stored, and analyzed.

Blood Tests Involve More Than Drawing Blood

Many people think the only important step is the blood draw itself. However, obtaining the sample is only the beginning.

Before blood test results reach a courtroom, the evidence typically passes through numerous stages, including:

• Collection of the sample
• Labeling and documentation
• Transportation
• Storage
• Laboratory processing
• Scientific analysis
• Reporting of the results

A mistake during any one of these steps may affect the reliability of the evidence.

Proper Chain of Custody Is Critical

Every person who handles a blood sample should properly document when they received it, where it was stored, and when it was transferred to another individual.

This documentation is known as the chain of custody.

Problems may arise if:

• Documentation is incomplete.
• Labels are incorrect.
• Samples are misplaced.
• Evidence changes hands without proper records.
• Storage locations are not documented.

If the prosecution cannot establish that the blood tested actually belonged to the defendant and remained secure throughout the process, the reliability of the evidence may be questioned.

Improper Storage May Affect the Sample

Blood samples must be stored under appropriate conditions to help preserve their integrity.

Storage problems may include:

• Incorrect temperatures
• Delayed refrigeration
• Broken containers
• Improper preservatives
• Exposure to contamination

Improper storage can potentially alter the chemical composition of the sample and affect laboratory testing.

Laboratory Errors Can Occur

Crime laboratories employ trained professionals, but they are not immune from human error.

Potential laboratory mistakes include:

• Sample mix-ups
• Data entry errors
• Equipment malfunctions
• Cross-contamination
• Improper testing procedures
• Calculation mistakes

Although laboratories maintain quality-control procedures, errors still occur. An experienced DWI defense attorney may examine laboratory records to determine whether problems existed during testing.

Fermentation May Increase Alcohol Levels

One lesser-known issue involves fermentation inside a blood sample.

If preservatives are not properly used or the sample is improperly stored, naturally occurring microorganisms may produce alcohol within the sample after it has been collected.

This process may artificially increase the reported alcohol concentration.

Proper collection techniques and laboratory procedures are intended to minimize this risk, but failures sometimes occur.

The Timing of the Blood Draw Matters

Blood is rarely drawn immediately after a traffic stop.

Instead, there may be a significant delay caused by:

• The roadside investigation
• Transportation to a medical facility
• Obtaining a search warrant
• Waiting for medical personnel
• Administrative procedures

Because alcohol is absorbed and eliminated over time, the blood alcohol concentration at the time of testing may differ from the concentration at the time the person was actually driving.

This timing issue can become an important consideration in certain DWI cases.

Medical Conditions May Affect Blood Test Interpretation

Certain medical issues may complicate how blood test results are interpreted.

Factors may include:

• Diabetes
• Liver disorders
• Certain prescription medications
• Medical treatments
• Recent surgeries
• Individual metabolic differences

Although a blood test may detect alcohol, interpreting what that result means requires consideration of numerous scientific and medical factors.

Search Warrants Must Be Legally Obtained

In many Texas DWI cases, officers obtain a search warrant before requiring a blood draw.

An attorney may review whether:

• The warrant was legally issued.
• Officers had probable cause.
• Proper procedures were followed.
• Constitutional rights were protected.

If legal violations occurred, challenges may be available regarding the admissibility of the blood evidence.

Scientific Evidence Should Never Be Accepted Without Review

Jurors often view laboratory evidence as highly reliable simply because it appears scientific.

However, blood testing depends on many assumptions, including that:

• The sample was properly collected.
• The correct blood was tested.
• Laboratory equipment functioned correctly.
• Scientists followed accepted procedures.
• Documentation remained accurate.

When those assumptions are challenged, the strength of the prosecution’s evidence may change significantly.

Every Blood Test Should Be Carefully Investigated

Blood test evidence often plays a central role in Texas DWI prosecutions, but it should never be accepted at face value.

An experienced Texas DWI defense attorney may thoroughly review:

• Collection procedures
• Search warrant documentation
• Chain of custody records
• Laboratory protocols
• Quality-control records
• Scientific testing methods
• Officer conduct during the investigation

Every case is different, and even small procedural mistakes may become important when building a defense. A careful investigation may uncover weaknesses that create opportunities to challenge the prosecution’s evidence and protect your future.

Call The Law Office of Alex Tyra, P.C. For Your Free Consultation

If you’ve been charged with DWI in Longview or anywhere in East Texas, don’t wait. The clock starts ticking the moment you’re arrested, and every decision you make from here on out matters. The Law Office of Alex Tyra, P.C. is ready to help you protect your future, your license, and your wallet.

Call us today at (903) 753-7499 to schedule your free consultation and take the first step toward fighting your DWI charges.