How to Challenge DWI Blood Test Results in Louisiana
Quick Summary
You can challenge DWI blood test results in Louisiana by reviewing the chain of custody, checking lab procedures and calibration records, requesting independent retesting, and filing a suppression motion when the evidence was improperly obtained or handled. A dwi blood test result is only as reliable as the process behind it, so each step in that process can be examined.
Request the full case file, including draw forms, evidence logs and lab intake records.
Look for missing signatures, time gaps, mismatched records and unrecorded storage temperatures.
Check whether the instrument was calibrated and quality control samples were run alongside the test.
Ask early for independent retesting, since samples can degrade or be used up.
File a suppression motion if the draw was unlawful or the testing did not meet required standards.
Table of Contents
Why Blood Test Results Are Open to Challenge
Last Updated: November 1, 2026
A dwi blood test can feel like the strongest evidence in a DWI case. A number comes back, and it seems to settle the question. But blood results depend on a long chain of handling, storage, testing and reporting, and each link can break. 337 Law, led by Marcus Myers, a former DWI special prosecutor, handles these cases and understands where the weak points usually are.
A blood alcohol concentration result is only as reliable as the process that produced it. Samples can be drawn incorrectly, stored improperly, mislabeled or tested on equipment that was not properly maintained. Any of these problems can give a defense attorney grounds to question the number.
Here is the good news. You do not have to accept the result at face value. This guide walks through the main ways a blood test can be challenged in Louisiana, step by step.
Step 1: Review the Chain of Custody for Your DWI Blood Sample
The chain of custody is the written record of who handled a blood sample, when, and where it was kept from the moment it was drawn until it was tested. A gap or inconsistency in that record is one of the most common grounds for challenge.
Start by requesting the full case file, including the draw form, evidence submission records and lab intake logs. Then look for:
Missing signatures or initials at any transfer point
Time gaps when the sample was not logged
Mismatched names, dates or case numbers
Storage temperatures that were not recorded or fell outside required ranges
Watch out: A single missing signature does not automatically win a case. A court looks at whether the gap creates a real doubt about the sample's integrity.
Many defense attorneys start here because chain of custody issues are often easy to document from the paperwork alone.
The article lists the most common problems to look for when reviewing a blood sample's chain of custody:
Problem | What to look for |
Missing signatures | Gaps or missing initials at any transfer point |
Time gaps | Periods when the sample was not logged |
Mismatched records | Names, dates or case numbers that do not match |
Storage issues | Temperatures not recorded or outside required ranges |
Step 2: Examine Blood Test Lab Errors in DWI Cases
Labs make mistakes. Testing equipment needs regular calibration, and analysts must follow strict procedures. When those steps are skipped or done poorly, results can be off.
Useful questions to ask include:
Was the testing instrument calibrated on the date of the test?
Did the lab run quality control samples alongside the defendant's sample?
Are the analyst's training and certification records current?
Were the lab's standard operating procedures followed exactly?
Lab records, instrument maintenance logs and proficiency test results can all be requested in discovery. A defense attorney can then review them for gaps or irregularities.
Step 3: Pursue Independent Blood Sample Retesting in DWI Cases
In some cases, the defense can ask for an independent test of a preserved sample. This can confirm or challenge the state's result. Whether retesting is possible depends on how the sample was stored and how much of it remains.
Retesting raises a few practical issues:
The sample must still be available and properly preserved
The independent lab must use accepted methods and proper controls
The timing matters, since samples can degrade if handled poorly
A common mistake is waiting too long to request retesting. Preservation requests should be made early, before the sample is used up or lost.
Step 4: File a Louisiana DWI Blood Test Suppression Motion
If the problems with the blood evidence are serious enough, the defense may file a motion to suppress. This asks the court to exclude the blood test result from trial because it was obtained or handled improperly.
A suppression motion generally argues one or more of these points:
The blood draw was not lawful, such as a lack of valid consent or a warrant issue
The sample was not handled in a way that protects its reliability
The testing procedures did not meet required standards
Louisiana courts decide these motions based on the specific facts of each case. The outcome depends heavily on the record, so the motion should be built on documented problems rather than general doubts.
Common Mistakes That Weaken a Blood Test Challenge
Several errors can undermine an otherwise strong challenge:
Waiting too long. Evidence can be lost, and deadlines for motions can pass.
Relying only on the number. Challenges work best when they combine several issues.
Ignoring the draw itself. How and when the blood was taken matters as much as the lab result.
Handling it alone. Reviewing lab records and procedures takes specialized knowledge.
A focused, well-documented challenge is generally more persuasive than a long list of weak objections.
Scheduling a Free Consultation to Review Your Blood Test Evidence
If you are facing a DWI charge built on a blood test, the time to act is early. 337 Law offers free telephone consultations, so you can discuss your blood test evidence and your options. Call the firm to schedule a conversation about your case and what a challenge might look like.
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Frequently Asked Questions
Can you challenge blood test results in a Louisiana DWI case?
Yes. A blood test result is not automatically conclusive in a Louisiana DWI case. Defense counsel can examine how the sample was drawn, labeled, stored, transported and analyzed, and can challenge whether the procedures followed Louisiana law and the testing laboratory's protocols. Challenges may lead to exclusion of the result or a weaker prosecution. Each case depends on its specific records, so a review of the full file is the only reliable way to assess the options.
What can make a DWI blood test inaccurate?
Several factors can affect accuracy, including improper sample collection, contamination, mislabeling, delays or improper storage, equipment calibration problems, and analyst error. Sample handling records and laboratory quality control documentation are often where these issues surface. Whether any of these problems occurred in a particular case can only be determined by reviewing the specific records and testing data.
Can a lab retest a blood sample in a DWI case?
Retesting is sometimes possible, but it depends on whether enough of the sample remains, the storage conditions, and the rules that apply to the case. Defense counsel may request access to the retained portion of the sample for independent analysis. Timing matters, so raising the request early in the case is important. Whether retesting is available and advisable in a specific matter should be discussed with a qualified Louisiana criminal defense attorney.
What should I do after a DWI arrest involving a blood test?
Contact a Louisiana criminal defense attorney as soon as possible so that evidence preservation requests and records demands can begin early. Avoid discussing the facts of the arrest with anyone other than your attorney. Write down what you remember about the arrest and the testing process while the details are fresh. Keep copies of any paperwork you received. Deadlines in DWI matters can be short, so prompt action helps protect your options.
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