I am Joel Brand, a California DUI defense attorney, and in this post I want to walk you through something that confuses a lot of people who just got arrested: you chose the blood test instead of the breath test, and now you are wondering what that actually means for your case. The answer matters more than most people realize, and understanding the process can help you and your attorney find angles that are not obvious at first glance.
Why People Choose the Blood Test
When law enforcement offers you the choice of a post-arrest chemical test, many drivers pick the blood draw because they believe it is more accurate, or because they heard the sample can be retested later. Both instincts have some truth to them. Unlike a breath machine, a blood sample is a physical piece of evidence that can be preserved and independently analyzed. That matters a great deal to a defense attorney.
What Happens at the Blood Draw
After your arrest, an officer will take you to a hospital, clinic, or jail where a trained phlebotomist draws your blood. The draw must follow specific protocols. The technician is supposed to use a non-alcohol swab, draw a sufficient volume, and place the sample into a properly labeled tube that contains a preservative and an anticoagulant. If any of those steps are skipped or done sloppily, the result can be challenged. I look at every one of those details when I take on a case.
How the Sample Is Stored and Transported
After the draw, the vial goes into a sealed evidence kit. That kit is supposed to be refrigerated and then sent to a crime laboratory, usually a law enforcement lab, for analysis. The chain of custody, meaning every person who handled the sample from the moment of the draw to the moment of testing, must be documented. A break in that chain is a serious problem for the prosecution. You can learn more about how the state documents this process in our article on the DMV discovery packet after a DUI.
The Laboratory Analysis
The lab will typically use a process called gas chromatography to measure the concentration of alcohol in your blood. This is a more reliable method than a roadside breath device, but it is not infallible. Instrument calibration, analyst training, contamination, and fermentation of the sample itself can all produce a falsely elevated result. Our library article on bad calibration as a DUI defense explains how equipment errors can affect your result, and the same principles apply to the lab equipment used on blood samples.
The Right to an Independent Blood Split
Here is one of the most important things I tell every client who chose the blood draw: you have the right to request that a portion of your blood sample, called a blood split, be sent to an independent laboratory of your choosing for retesting. This right is protected under California law. If the independent result differs from the state lab result, that discrepancy becomes a powerful piece of defense evidence. You should ask your attorney about this as soon as possible, because blood samples do not last forever and the request needs to be made before the sample degrades.
Rising BAC and the Blood Test
One defense that applies specifically to blood draws is the rising BAC argument. Alcohol continues to absorb into your bloodstream for a period of time after your last drink. If there was a meaningful gap between when you were driving and when your blood was actually drawn, your BAC at the time of the draw may have been higher than your BAC at the time you were behind the wheel. Our article on the rising BAC defense explains this concept in detail. A blood draw that happens an hour or more after the traffic stop can actually work in your favor for this reason.
Fermentation and Contamination of the Sample
If blood is not stored correctly, bacteria in the sample can produce alcohol through fermentation, causing the measured BAC to be higher than it truly was at the time of the draw. Similarly, if the preservative or anticoagulant in the collection tube was insufficient, or if the tube was contaminated, the result can be skewed. These are not hypothetical arguments. They come up in real cases, and they are worth investigating. I often work with forensic toxicology experts who can review the lab's handling procedures and flag any irregularities.
How Your Blood Result Connects to the DMV Side of Your Case
Remember that a DUI arrest in California triggers two separate proceedings: the criminal court case and the DMV administrative hearing. The blood result will be used in both. On the DMV side, the state will rely on the result reported in your DS-367 form to suspend your license. Understanding how errors in that form can affect your case is covered in our article on DS-367 mistakes that can help your DUI case. On the court side, the prosecutor will introduce the lab report as evidence at trial or use it as leverage in plea negotiations.
What a High Result Means for Your Defense Strategy
If your blood result came back above 0.15 percent, the prosecution may seek enhanced penalties under California law. Our article on high BAC DUI at 0.15 and above explains what those enhancements look like. A high result does not mean the case is over. It means the defense strategy needs to be thorough. Every link in the chain from the traffic stop to the lab report is a potential weak point.
What About the Police Mistakes Before the Draw
Even if your blood result is technically valid, the evidence can sometimes be suppressed if law enforcement violated your rights before or during the arrest. A motion to suppress evidence under California law can exclude the blood result entirely if the stop, detention, or arrest was unlawful. Our library covers this in detail in the article on 1538.5 motions to suppress evidence in a DUI trial. I also encourage you to read about the most common mistakes police make at a DUI stop, because those errors do not disappear just because a blood test was taken afterward.
What You Should Do Right Now
If you chose the blood test, your job right now is to preserve your options. Do not assume the result is the final word. Do not assume a high number means you have no defense. Write down everything you remember about the stop, the arrest, the blood draw, and the timeline of your drinking that night. Then get that information to a defense attorney who can evaluate it against the discovery documents the state will eventually produce.
You can get a free written case analysis on this page. Call me directly at (888) 271-6644. I answer my own phone, 24/7. This post is general information and is not a guarantee of any outcome in your case. For more on California DUI law, visit more from the DUI blog.