A false high BAC blood test can be caused by improper handling, contamination, medical conditions, fermentation in the sample, or testing errors at the lab. Even small mistakes in collection or storage can artificially increase the reported blood alcohol concentration.
When you are facing a DUI in California, a blood test result may look definitive. In reality, it is only as reliable as the process behind it. We regularly review how the sample was drawn, preserved, transported, and analyzed, because each step matters.
Can a Blood Test for DUI Be Wrong?
Yes. While blood tests are often considered more accurate than breath tests, they are not immune to error. In California DUI cases, the prosecution must show that the test was properly administered and that the result is trustworthy.
Problems can arise at multiple stages:
- During the blood draw
- While the sample is stored or transported
- At the crime lab during testing
- When results are reported or interpreted
If any part of the chain is flawed, your BAC reading may not reflect your true alcohol level at the time of driving.
Improper Blood Collection Procedures
California law requires that blood be drawn in a medically approved manner. If the person collecting the sample fails to follow protocol, contamination can occur.
Common issues include:
- Failing to properly mix preservatives and anticoagulants in the vial
- Drawing blood in a non-sterile environment
- Using improperly stored or expired collection equipment
If any of these steps are handled incorrectly, the integrity of the sample may be compromised before it ever reaches the lab.
Fermentation and Improper Storage
One of the most overlooked causes of a falsely elevated BAC is fermentation inside the vial. Blood samples are typically preserved with chemicals designed to prevent microbial growth. If those preservatives are missing, expired, or not properly mixed, bacteria can produce alcohol within the tube. This process can artificially increase the alcohol concentration, even after the sample leaves your body.
Storage also matters. Blood samples should be refrigerated. If a sample sits at room temperature for too long, chemical changes may occur that affect the final reading.
We often examine:
- How long the sample sat before testing
- Whether it was properly refrigerated
- Whether the preservative levels were documented
Lab Errors and Testing Mistakes
Crime labs rely on complex machines, often using gas chromatography to measure alcohol content. These machines must be calibrated and maintained regularly.
Errors may include:
- Improper calibration
- Contaminated testing equipment
- Sample mislabeling
- Technician mistakes during analysis
If the machine is not properly maintained, results can drift upward. If samples are mislabeled, you could be looking at someone else’s BAC.
In a DUI case, we can request maintenance logs, calibration records, and analyst notes to determine whether the reported number can be trusted.
Medical Conditions That Can Affect BAC Results
Certain medical conditions can influence how alcohol appears in your blood. For example:
- Diabetes, particularly if it leads to elevated ketones
- Gastroesophageal reflux disease, which can affect breath testing and may raise related evidentiary issues
While these conditions are not common defenses, they may become relevant depending on your medical history. Each case is fact-specific.
Rising Blood Alcohol and Timing Issues
A blood test does not measure your BAC at the time you were driving. It measures your BAC at the time your blood was drawn.
Alcohol absorbs into the bloodstream over time. If you were tested an hour or more after a traffic stop, your BAC may have been lower while you were actually behind the wheel.
This is known as a rising blood alcohol defense. Prosecutors sometimes use retrograde extrapolation to estimate earlier levels, but that process relies on assumptions about when you drank, what you ate, and how your body metabolizes alcohol.
We scrutinize those assumptions carefully.
Why Challenging a Blood Test Can Matter
In California, a BAC of 0.08 percent or higher can support a DUI charge. But the number alone does not end the case. If the blood result is unreliable, the foundation of the prosecution’s evidence weakens.
When we defend a DUI case, we look beyond the surface. We analyze the paperwork, lab procedures, and scientific methods used to produce the result. If something does not add up, we raise it.
Your Defense Starts With Asking the Right Questions
A high BAC result does not automatically mean the test was accurate. Collection errors, storage problems, lab mistakes, and timing issues can all lead to falsely elevated readings.
If you have been charged with DUI in California, we can review your case, examine the blood test process, and identify potential weaknesses in the evidence. Contact the Law Offices of Johnson & Johnson to discuss your situation and learn how we can help you move forward with a clear defense strategy.