Menu Close Menu

How to challenge a blood test in DUI cases?

DUI blood tests are not as conclusive as they seem… even when they show a BAC of .08% or higher, or indicate the presence of drugs.

When you drive in California, you give your implied consent to chemical tests if you are lawfully arrested for drunk driving and/or DUI of drugs.

Blood tests are generally considered more reliable to establish blood alcohol content (BAC) than BAC breath tests. They are also -- at least, at present -- the only court-admissible tests in California for DUI of drugs.

But blood testing is not error-proof.  An experienced California DUI attorney knows this and can use it to attack your DUI blood test results.

1.    How California DUI Blood Tests Produce False Results

Title 17 of the California Code of Regulations sets forth strict protocols for collecting and processing DUI blood samples. If even one of these regulations is not followed, the results of your DUI blood test are open to challenge.

Mistakes involved in the collection and processing of DUI blood samples include:

  • Your blood was drawn too long after your arrest,
  • There were not enough anticoagulants or preservatives in the vial to prevent:
    • fermentation,
    • contamination, or
    • clotting
  • The anticoagulants and preservatives were not adequately mixed with your blood,
  • The person who drew your blood was not properly trained,
  • Alcohol was used to sterilize the draw site,
  • The sample was improperly stored,
  • The sample was lost or destroyed,
  • There are gaps in the chain-of-custody of the sample, or
  • The instruments for measuring BAC or the presence of drugs were not properly calibrated.

2.    Preservation of the Sample for Future Testing (“Blood Splits”)

Title 17 requires law enforcement in a DUI case to collect enough blood so that it may be tested at least twice. This is to give you the opportunity to have your blood independently tested by a lab of your own choosing.

Legally, your blood must be kept for at least one year from the date it was collected.  During that time, your DUI defense lawyer can file what is known as a "blood split" motion. The laboratory or government agency having custody of your blood must then turn over a portion of the blood collected after your DUI arrest.

Contestable errors relating to “blood splits” include:

  • There was not enough blood drawn to allow for a blood split,
  • The sample was not retained for at least one year, or
  • The government failed to timely provide you a portion of the sample as legally required.

3. A High BAC Doesn't Always Mean You Drove Drunk

It can take anywhere from 50 minutes to several hours for alcohol to be absorbed fully by your system. As a result, blood alcohol levels continue to rise even after you have stopped drinking.

This means that your BAC could have been rising between the time you were arrested and the time your blood was drawn. Even if your BAC was above the legal limit at the time of your test, it might not have been at the time you drove.

4.    Additional Problems with Blood Testing for DUI of Drugs

Unlike alcohol, there is no “per se” amount of drugs in the bloodstream that can be used to establish impairment.  DUI blood tests typically screen for a drug's presence -- not its amount.

DUI blood tests cannot establish:

  • how much of a drug you consumed,
  • how recently you consumed it, or
  • whether the amount was enough to cause you to drive impaired.

Don't despair because a DUI blood test “proved” you were drunk or high.  Our Southern California DUI lawyers understand the many ways that blood tests can be wrong. We know what questions to ask and what signs to look for.

Our attorneys have successfully challenged blood tests results for clients throughout Los Angeles, San Bernardino, Riverside, Ventura and Orange Counties. Contact us today for a free consultation.

A “positive” blood test does not always mean a negative result.

Southern California DUI Defense


DUI cases are rarely hopeless. DUI convictions are almost never inevitable. Clients retain our California DUI defense attorneys for one reason: they want to fight the case. And win.

Contact Us For Help

The police arrested you for DUI. You gave a blood or a breath sample. The DUI officer confiscated you drivers license. The police released you with a notice to appear in court in a few weeks. Where do you go from here? Our lawyers are here to guide you step by step.