Challenging Blood Test Results

Scientific and Strategic Defenses for Blood Test DUI Cases

Challenging Blood Test Results in Colorado DUI Cases

Blood test evidence is often viewed as some of the strongest evidence in a Colorado DUI prosecution. In many cases, prosecutors rely heavily on blood alcohol or toxicology results when pursuing DUI, DUI per se, or drug-related driving charges. However, blood test results are not automatically accurate, infallible, or immune from challenge. Our DUI Defenses in Colorado resource discusses how evidentiary issues, constitutional violations, and scientific challenges may affect DUI prosecutions.

At The Lawrence Law Firm, we carefully evaluate the reliability of blood testing evidence in every DUI and DUID case. While chemical testing can be important evidence, it is still only one part of the prosecution’s overall case and must be evaluated alongside officer observations, body-worn camera footage, admissions, and the surrounding circumstances.

Blood Tests Are Often Central to Colorado DUI Cases

Blood testing is commonly used in Colorado DUI investigations involving:

alcohol-related DUI charges,
marijuana DUI allegations,
prescription drug DUI cases,
DUI refusals,
and serious injury or accident investigations.

Unlike breath testing, which estimates blood alcohol concentration through breath samples, blood testing involves laboratory analysis of an actual blood sample.

Because of this, juries often view blood evidence as especially reliable or scientific.

However, blood testing still involves:

collection procedures,
handling protocols,
chain of custody requirements,
laboratory analysis,
and interpretation issues.

Problems at any stage of the process may potentially affect reliability.

Blood Test Results Are Not the Entire DUI Case

One important reality in DUI litigation is that blood test evidence is not the entirety of the state’s case.

Even in cases involving elevated blood alcohol results, prosecutors still commonly rely on:

admissions regarding drinking,
driving behavior,
field sobriety test performance,
officer observations,
demeanor,
speech patterns,
balance issues,
and body-worn camera footage.

In many DUI trials, jurors evaluate the entire encounter shown on video rather than focusing solely on the chemical result itself.

That is why challenging a blood test does not automatically mean the case will be dismissed. Instead, blood test challenges may:

weaken the prosecution’s evidence,
create reasonable doubt,
reduce sentencing exposure,
improve plea negotiations,
or affect aggravating sentencing allegations.

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Blood Draw Procedures Matter

Blood testing in Colorado typically involves:

Collection of the blood sample,
Packaging and preservation,
Transportation,
Laboratory testing,
Reporting and interpretation.

Each stage presents potential issues that may affect reliability or admissibility.

Defense attorneys often review:

police reports,
laboratory records,
chain of custody documentation,
toxicology reports,
and bodycam footage
when evaluating blood testing evidence.

Common Defenses to Blood Test Results

Chain of Custody Issues

The prosecution must generally establish that the blood sample tested actually belonged to the defendant and was properly handled throughout the process.

Potential issues may include:

incomplete documentation,
labeling errors,
transfer irregularities,
storage problems,
or gaps in handling procedures.

Chain of custody problems may affect reliability and evidentiary weight.

Fermentation and Improper Preservation

Blood samples must typically be preserved and stored correctly to reduce the risk of fermentation or contamination.

Improper handling may potentially affect alcohol concentration results.

Potential issues can involve:

preservative failures,
improper storage temperatures,
delayed testing,
or contamination concerns.

In some cases, delayed testing may also raise issues involving rising blood alcohol concentration and whether the reported BAC accurately reflected the defenadnt’s BAC at time of driving.

Fermentation and Improper Preservation

Blood samples must typically be preserved and stored correctly to reduce the risk of fermentation or contamination.

Improper handling may potentially affect alcohol concentration results.

Potential issues can involve:

preservative failures,
improper storage temperatures,
delayed testing,
or contamination concerns.

Laboratory and Testing Errors

Blood testing involves scientific analysis performed by human beings and laboratory equipment.

Potential issues may include:

testing irregularities,
analyst error,
contamination,
improper calibration,
incomplete documentation,
or deviations from established procedures.

In some cases, defense attorneys may review:

toxicology records,
laboratory protocols,
analyst certifications,
and quality assurance documentation.

Laboratory and Testing Errors

Blood testing involves scientific analysis performed by human beings and laboratory equipment.

Potential issues may include:

testing irregularities,
analyst error,
contamination,
improper calibration,
incomplete documentation,
or deviations from established procedures.

In some cases, defense attorneys may review:

toxicology records,
laboratory protocols,
analyst certifications,
and quality assurance documentation.

Blood Tests in Marijuana and Drug DUI Cases

Blood testing plays a particularly important role in Colorado marijuana and drug-related DUI prosecutions.

Unlike alcohol cases, many DUID prosecutions involve:

subjective observations,
toxicology interpretation,
and disputes regarding actual impairment.

For example:

the presence of THC in blood does not automatically prove a driver was impaired at the time of driving,
and regular marijuana users may retain detectable THC levels long after actual impairment has ended.

Similarly, prescription medication cases often involve disputes over:

lawful medical use,
dosage timing,
tolerance,
and whether observed behavior was actually caused by impairment.

These cases frequently become highly fact-specific.

DUI vs. DWAI: Why Blood Test Challenges Still Matter

Even if a jury questions the reliability or significance of a blood test result, prosecutors may still pursue a lesser DWAI theory at trial.

Under Colorado law:

Driving Under the Influence (“DUI”) generally involves substantial impairment,
while
Driving While Ability is Impaired (“DWAI”) requires impairment “to the slightest degree.”

The phrase “slightest degree” is extremely broad and often gives prosecutors substantial flexibility in arguing impairment.

Because of this, prosecutors may still rely on:

officer observations,
admissions,
driving conduct,
and body-worn camera footage,
even where the chemical evidence itself is disputed.

This means DUI trials are often about much more than simply the BAC number.

Elevated Blood Alcohol Results Can Significantly Affect Sentencing

Even where prosecutors continue pursuing a DWAI theory, challenging elevated blood alcohol results may still be extremely important.

In Colorado, higher BAC allegations may affect:

mandatory jail exposure,
sentencing negotiations,
probation conditions,
treatment requirements,
and aggravating sentencing factors.

For example, BAC allegations of .15 or higher can trigger enhanced penalties and mandatory consequences in many cases.

Because of this, reducing the reliability or weight of the blood test result may still substantially affect the outcome of the case.

Body-Worn Camera Evidence Often Becomes Extremely Important

In many DUI and DUID trials, body-worn camera footage becomes one of the most influential forms of evidence.

Jurors often evaluate:

coordination,
speech,
demeanor,
responsiveness,
balance,
and overall appearance.

This is why blood test litigation is rarely isolated from the rest of the investigation.

Even in cases involving elevated blood results, jurors may compare:

the toxicology evidence,
the officer’s testimony,
and the defendant’s actual appearance on video.

Effective DUI defense often requires analysis of the entire investigation—not just the laboratory result alone.

Blood Test Cases Frequently Involve Technical Litigation

Litigating blood testing issues may involve review of:

toxicology reports,
laboratory records,
chain of custody documentation,
collection procedures,
bodycam footage,
analyst certifications,
and scientific evidence.

These issues may arise during:

suppression hearings,
evidentiary motions,
negotiations,
or trial.

Speak With a Colorado DUI Defense Attorney

If you were arrested for DUI or DUID in Colorado, it is important to understand that blood testing evidence is only one part of the prosecution’s case. Officer observations, video evidence, testing procedures, and scientific reliability may all affect the outcome.

At The Lawrence Law Firm, we represent clients charged with DUI, DWAI, felony DUI, and drug-related driving offenses throughout the Denver metro area.

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