Forensic Science
Blood Testing in DUI Cases: Chain of Custody, Fermentation & Coagulation Defenses
Legal Counsel Review: Senior DUI Trial Attorney & Forensic Specialist•Published: September 2, 2026•Statutory Jurisdiction: State & Federal Courts
While prosecutors present blood test results as definitive scientific evidence, forensic toxicology laboratories are subject to biological degradation, improper anticoagulant ratios, and fatal chain of custody gaps.
1. Physiological & Biochemical Blood Defenses
| Biochemical Mechanism | Forensic Pathology Cause | Impact on Blood BAC Reading |
|---|---|---|
| Endogenous Ethanol Fermentation | Absence of sufficient Sodium Fluoride preservative allows Candida albicans yeast to convert glucose into alcohol in the test vial | Falsely inflates blood alcohol by 0.04% to 0.10%+ |
| Blood Clotting / Coagulation | Inadequate Potassium Oxalate anticoagulant causes fibrin clotting, leaving alcohol concentrated in serum | Serum testing yields readings 15% to 20% higher than whole blood |
| Sterilization Contamination | Phlebotomist wipes injection site with isopropyl alcohol swab rather than non-alcoholic betadine | Direct sample contamination during vacuum needle insertion |
| Chain of Custody Breaks | Blood vials stored at room temperature without refrigeration for days before GC-FID analysis | Suppresses test results under Title 17 regulations |
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Authored & Verified by Duiattorneysonline Senior Trial Counsel
Our legal research desk analyzes Title 17 forensic compliance standards, NHTSA standardized field sobriety test administration manuals, DMV administrative per se hearing precedents, and Fourth Amendment search and seizure suppression strategies.