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Blood Test Defense in DUI Cases
Blood tests are widely considered more reliable than breath tests, but they are not unchallengeable. Procedural and scientific issues can reduce or eliminate the weight of blood evidence.
How DUI blood draws work in California
After arrest, you can choose between breath or blood (and sometimes urine) testing. If you refuse or are unconscious, the officer typically obtains a warrant for a forced blood draw.
Common blood test defenses
1. Warrant defects
If the blood draw was warrantless and no exception applies (consent, exigency), the result may be suppressed under the Fourth Amendment.
2. Chain of custody
Every person who handled the blood — phlebotomist, transporter, lab technician — must be documented. Gaps in chain of custody undermine evidentiary value.
3. Fermentation
Blood vials contain anti-coagulant (potassium oxalate) and preservative (sodium fluoride). If preservative levels are insufficient, blood can ferment in the vial — producing alcohol and inflating BAC results.
4. Storage temperature
Blood samples should be refrigerated within hours. Improper storage can cause fermentation or degradation.
5. Lab errors
California crime labs are not infallible. Switched samples, contaminated equipment, and mathematical errors do occur. An expert witness can challenge specific lab procedures.
6. Title 17 violations
California Code of Regulations Title 17 also governs blood draws — proper site preparation (no alcohol swab), proper personnel (licensed phlebotomist), and proper timing.
Independent retesting
You have the right to request an independent test of your blood sample. The original sample is typically retained for 1 year. An independent lab analysis can confirm or refute the original result.
Facing DUI blood test evidence? Contact us for an experienced defense.
Frequently Asked Questions
Can a DUI blood test be wrong?
Yes. Blood tests can be challenged on many grounds: improper collection, fermentation in the vial, contamination, chain of custody breaks, lab errors, and warrant requirements. Even small procedural failures can suppress the result.
Does a DUI blood draw require a warrant in California?
After Birchfield v. North Dakota (2016) and Mitchell v. Wisconsin (2019), warrantless blood draws are allowed only in narrow circumstances (consent, exigency, or unconscious driver). Without a warrant or recognized exception, the blood evidence may be suppressed.
How long does a DUI blood test take to come back?
Typically 4–8 weeks. Until results return, the criminal case may proceed on other evidence. The DMV hearing often happens before blood results are available.
Can I refuse a blood test in California?
You have a limited right to refuse, but refusal triggers automatic license suspension under California's implied consent law. After arrest with probable cause for DUI, you must submit to chemical testing or face a 1-year suspension (first refusal).
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