Can You Challenge a Blood Test in a Missouri DWI Case?

Blood tests are often presented as definitive proof in DWI cases. Prosecutors treat BAC results from blood draws as irrefutable scientific evidence that someone was driving while intoxicated. But blood tests are not infallible, and Missouri law provides multiple grounds for challenging their accuracy and admissibility.

When Blood Tests Are Used in Missouri DWI Cases

Under Missouri Revised Statutes § 577.020, law enforcement can request chemical testing of breath, blood, saliva, or urine when someone is arrested for DWI. Blood tests typically occur in specific situations:

• When the person is unconscious or unable to provide a breath sample
• When there’s a serious injury or fatality collision
• When the person agrees to a blood test instead of a breath test
• When law enforcement obtains a search warrant for blood
• When the person is suspected of drug impairment (not just alcohol)

The statute requires that blood tests be “performed, according to methods approved by the state department of health and senior services, by licensed medical personnel or by a person possessing a valid permit issued by the state department of health and senior services.”

Constitutional Challenges to Blood Draws

Warrantless Blood Draws

The Missouri Court of Appeals addressed warrantless blood draws in State v. Osborn, 591 S.W.3d 1 (Mo. App. W.D. 2019). The court held:

“Implied consent provisions of this section and section 577.033 do not permit warrantless blood draws from unresponsive subjects in criminal cases, absent evidence of exigent circumstances.”

This means law enforcement generally cannot draw blood without a warrant, even from unconscious DWI suspects, unless true exigent circumstances exist. Implied consent under § 577.020 does not override the Fourth Amendment’s warrant requirement.

Common constitutional challenges include:

• Lack of warrant: If blood was drawn without a warrant and without valid exigent circumstances, the evidence may be suppressed under the Fourth Amendment.
• Invalid consent: Even when someone consents to a blood draw, that consent must be knowing and voluntary. Coerced consent or consent obtained through threats of enhanced penalties may be invalid.
• Improper search warrant: If law enforcement obtained a warrant, the warrant must be supported by probable cause and properly executed. Defects in the warrant or its execution can lead to suppression.

Procedural and Technical Challenges

Chain of Custody Issues

Blood evidence must maintain an unbroken chain of custody from collection through testing.

Common chain of custody problems include:

• Missing documentation of who handled the sample at each stage
• Unexplained gaps in the timeline of sample transfer
• Improper storage conditions between collection and testing
• Lack of evidence that the sample was sealed and labeled correctly

Testing Methodology Requirements

Under § 577.020(3), blood tests must follow methods approved by the Missouri Department of Health and Senior Services. The department establishes standards for:

• Approved testing techniques and equipment
• Qualifications of individuals performing tests
• Proper collection and storage procedures
• Quality control measures

If testing didn’t follow approved methods, the results may be inadmissible or unreliable.

Blood Collection Procedures

Blood must be drawn using proper antiseptic procedures. Alcohol-based antiseptics can contaminate the sample and artificially elevate BAC readings. Proper procedure requires using non-alcohol antiseptics like betadine or benzalkonium chloride.

Additionally, blood samples must contain proper preservatives (sodium fluoride) and anticoagulants (potassium oxalate) to prevent fermentation and clotting. Improper preservative levels can cause the sample to ferment, creating alcohol that wasn’t present when the blood was drawn.

Laboratory Errors

Crime labs and private testing facilities can make mistakes:

• Using improperly calibrated equipment
• Failing to follow standard operating procedures
• Contaminating samples
• Transcription errors in recording results
• Using expired testing reagents

Medical Conditions Affecting Blood Test Results

Certain medical conditions can affect blood alcohol readings:

• Diabetes and ketoacidosis: Can produce isopropyl alcohol that some testing methods may detect as ethanol
• GERD and acid reflux: May affect fermentation rates in blood samples if not properly preserved
• Hematocrit levels: Blood with abnormal red blood cell counts can produce inaccurate BAC readings

An experienced St. Louis DWI attorney will review medical records to identify conditions that might have affected test accuracy.

Timing and Retrograde Extrapolation Issues

Blood tests don’t show BAC at the time of driving – they show BAC at the time blood was drawn. In Missouri, there’s often a significant delay between the traffic stop and blood collection, especially when a warrant is required.

If someone’s BAC was rising at the time of the stop (still absorbing alcohol), their BAC when blood was drawn could be higher than when they were actually driving. This is called retrograde extrapolation, and it requires expert testimony to establish what someone’s BAC actually was at the time they were operating the vehicle.

The Right to an Independent Test

Under § 577.020(5), anyone who submits to blood testing has the right to request their own independent test:

“The person tested may have a physician, or a qualified technician, chemist, registered nurse, or other qualified person at the choosing and expense of the person to be tested, administer a test in addition to any administered at the direction of a law enforcement officer.”

If law enforcement interfered with this right, or if the person’s independent test showed different results, this creates additional grounds to challenge the state’s blood evidence.

Access to Testing Information

Section 577.020(6) requires that “full information concerning the test shall be made available” upon request. This includes:

• The type of test and procedures followed
• Time of sample collection
• Numerical BAC results
• Type and status of the tester’s permit
• Maintenance records for testing equipment

However, the statute specifically states that “full information does not include manuals, schematics, or software of the instrument used to test the person or any other material that is not in the actual possession of the state.”

This limitation can make it difficult to fully evaluate testing procedures, but experienced attorneys know how to obtain necessary discovery through other means.

Expert Witnesses in Blood Test Cases

Successfully challenging blood test results often requires expert testimony. Forensic toxicologists can testify about:

• Whether proper collection procedures were followed
• Whether testing methodology was appropriate
• Whether results are scientifically reliable
• How medical conditions or timing issues affected results
• Whether alternative explanations exist for the BAC reading

Blood Test Evidence Can Be Challenged With the Right Attorney

A blood test result is not the end of a DWI case. Multiple legal, procedural, and scientific grounds exist for challenging blood evidence, from constitutional violations to laboratory errors to medical conditions affecting results.

If someone is facing DWI charges based on blood test evidence, they should contact an experienced criminal defense attorney immediately. The sooner an attorney can begin investigating the blood draw procedures, testing methodology, and potential defenses, the better the chances of successfully challenging the evidence.

Your defense starts with a conversation.