Beat a Mississippi DUI: How to Challenge Breath and Blood Tests

Why Chemical Test Results Are Not the Final Word

Mississippi DUI prosecutions often rely on Intoxilyzer breath readings or blood draws to prove impairment or an unlawful alcohol concentration. See Miss. Code Ann. § 63-11-30. These tests are only as reliable as the people, procedures, and equipment behind them. To admit chemical test results, the State generally must show the test was performed by a permitted operator using methods approved by the Mississippi Forensics Laboratory and in compliance with applicable rules. See Miss. Code Ann. § 63-11-19; Miss. R. Evid. 901. If those foundations are not met, courts may exclude the results or a jury may give them less weight.

Breath Tests: Key Weak Points

• Approved instruments and maintenance: Breath testing must use an approved instrument and comply with the State Crime Lab’s approved methods. Maintenance and performance records matter. See § 63-11-19.
• Calibration and accuracy checks: The State should document periodic accuracy verifications and any corrective actions if the instrument drifted out of tolerance.
• Operator permits and procedures: The person administering the test must have a valid permit and follow the approved method. See § 63-11-19.
• Observation/deprivation period: The approved method generally requires an observation period to reduce the risk of mouth alcohol contamination.
• Mouth alcohol and medical conditions: GERD/acid reflux, recent vomiting, or dental work can trap alcohol in the mouth and skew readings. NHTSA recognizes mouth alcohol as a concern; see NHTSA SFST resources.
• Environmental or electronic interference: Improper device placement, temperature extremes, or electronic interference may introduce error when supported by evidence.
• Multiple or inconsistent samples: Aborted sequences or materially inconsistent blows can indicate unreliable data.
• Documentation gaps: Missing logs, operator permits, simulator solution records, or status reports can undermine the State’s foundation.

Blood Tests: Chain of Custody and Lab Protocols

• Legal basis for the draw: Blood draws generally require valid consent or a warrant consistent with Birchfield v. North Dakota, 579 U.S. 438 (2016), unless another recognized exception applies.
• Qualified personnel and approved kits: Statute addresses who may withdraw blood and that testing must follow methods approved by the State Crime Lab. See § 63-11-19.
• Chain of custody: The State must authenticate the sample through testimony or records showing a reasonable probability the evidence was not altered or tampered with. See Miss. R. Evid. 901.
• Lab accreditation and methods: Defense review often includes instrument validation, maintenance logs, calibration curves, controls, and adherence to SOPs.
• Fermentation/contamination risks: Inadequate preservatives, improper sealing, or prolonged warm storage may cause fermentation that can elevate measured alcohol.
• Reporting and uncertainty: Chromatograms, quality control results, and stated measurement uncertainty inform how much weight a result should be given.

Implied Consent and Refusal Issues

Mississippi’s implied consent law deems drivers to have consented to chemical testing after a lawful DUI arrest, but officers must still follow statutory procedures and provide required advisements. See Miss. Code Ann. § 63-11-5. Refusals can trigger license consequences under § 63-11-23. Failures in advisements, consent, or warrant steps may support suppression of a test result, particularly for blood draws after Birchfield.

Medical and Physiological Defenses

Certain conditions can produce high or erratic readings without true impairment: GERD/hiatal hernia, diabetes with elevated ketones, low-carb/fasting diets, elevated body temperature, or residual mouth alcohol. Modern instruments include filters and safeguards, but they are not infallible; the defense may use medical records and expert testimony to explain anomalies. See general discussion in NHTSA SFST materials.

Field Sobriety Tests and Probable Cause

Before chemical testing, officers rely on driving observations and field sobriety tests. If the stop, detention, or arrest lacked legal justification, downstream evidence including breath or blood results may be suppressed as fruit of the poisonous tree. See Terry v. Ohio, 392 U.S. 1 (1968) and Wong Sun v. United States, 371 U.S. 471 (1963). Departures from standardized SFST guidance can also affect weight. See NHTSA SFST.

Strategic Motions to Suppress or Limit Evidence

• Suppression motions: Challenge the lawfulness of the stop, arrest, advisements, consent, or warrant process.
• Foundational challenges: Seek exclusion for noncompliance with § 63-11-19 or for authentication gaps under MRE 901.
• Limit expert overstatements: Use MRE 702 and Mississippi reliability caselaw such as Miss. Transp. Comm’n v. McLemore, 863 So. 2d 31 (Miss. 2003) to prevent unsupported opinions.
• Compel records: Subpoena maintenance logs, operator permits, simulator solution records, lab SOPs, validation data, and uncertainty documentation.

Practical Tips

Quick Checklist

FAQ

Can I refuse a breath or blood test in Mississippi?

Refusal is possible but can trigger license consequences under implied consent law. See § 63-11-23. Talk to a lawyer about your specific facts.

Do police need a warrant for a blood draw?

Usually yes, unless you gave valid consent or another exception applies. See Birchfield.

What if the machine was not properly maintained?

Gaps in maintenance, calibration, or documentation can support exclusion or reduced weight of the result.

Will medical conditions affect my case?

Conditions like GERD or diabetes can introduce mouth alcohol or endogenous compounds that affect readings. Expert input can help explain anomalies.

Next Steps

If you are facing a Mississippi DUI based on breath or blood results, consult counsel promptly. Bring any paperwork from your arrest, information about medical conditions, and the timeline of your last food and drink. A focused review can identify the most promising challenges.

Talk to a Mississippi DUI defense lawyer: Request a consultation.

Mississippi-specific disclaimer: This article provides general information about Mississippi DUI law and procedure and is not legal advice. Laws change, and outcomes depend on specific facts. Reading this page does not create an attorney-client relationship. Consult a licensed Mississippi attorney about your situation.