DUI Blood Testing: How to Challenge Blood Test Results in Your DUI Case


DUI blood tests are prone to a variety of errors that can be challenged in court. In California, the procedures for DUI blood draws and testing are set forth in Title 17 of the Code of Regulations.1If these rules are violated, the results of the blood test may be invalid.

Mistakes that can produce unreliable blood alcohol concentration ("BAC") results include:

  • Contamination of the sample after it is collected,
  • Switched or intermingled samples, or
  • Fermentation, which can cause the sample to produce alcohol inside the vial.

To help you better understand DUI blood samples and testing, our California DUI defense lawyers discuss the following, below:

Scientist holding up blood vial california dui and bloodtest legal help
Many experts consider blood tests the most accurate way to measure blood alcohol concentration (BAC) in a California DUI case.

1. When is a DUI blood test required in California law?

People who drive in California are deemed to have consented to take a DUI blood test or DUI breath test if they are lawfully arrested for driving under the influence.2 This is known as California's “implied consent” law.

Drivers must usually be given the choice of whether to take a breath or a blood test.3 Exceptions are when:

  • The officer has reasonable cause to believe the driver was driving under the influence of a drug (“DUID”), in which case a blood test can be required;4
  • The driver is unconscious (or deceased);5 or
  • The driver has been taken to a medical facility where breath testing equipment is not available.6

2. Is it better to take a DUI blood test or breath test?

Most people elect to take a breath test. DUI breath testing is faster and less invasive. (Note that motorist may also be asked to undergo a mouth swab test as part of the DUI investigation.)

But not everyone can take a breath test. For instance, people with medical problems such as asthma or emphysema may not be able to blow hard enough.

Other people may be unconscious, either from alcohol and/or drugs or as the result of an accident.

Is a blood test ever preferable?

Some drivers may prefer a DUI blood test. Blood tests directly measure the amount of alcohol in someone's bloodstream.

Breath testing devices measure the amount of alcohol in deep lung air. They then mathematically convert this to an approximately equivalent BAC.

The formula for this conversion (known as a “partition ratio”) is fixed by law. But, in reality, every individual's partition ratio is different. So, some people consider blood tests a more accurate measure of BAC than breath.7

Also, with a blood test, a portion of the sample can be saved for later retesting, as discussed in Section 6, below. This is the major advantage of taking a blood test for BAC rather than a breath test.

3. What are the Title 17 regulations?

Title 17 of the California Code of Regulations sets forth the procedures that govern DUI chemical tests. It includes general requirements for testing labs as well as procedures for blood tests specifically.

Under Title 17, regulations that apply to the testing of blood include:

  • A specified technician or medical professional must draw the blood as soon as possible after an alleged offense.8
  • The draw site must be sterilized with something other than an alcohol-based product (to avoid adding external alcohol to the sample).9
  • There must be an anticoagulant and a preservative in the vial to prevent contamination and/or clotting.10
  • Any reusable equipment may not be cleaned with or kept in alcohol or other volatile organic solvents.11
  • The identity and integrity of the sample must be maintained throughout each step so that chain-of-custody is recorded and undisturbed.12

If any of these or other protocols are not followed, the accuracy of the DUI blood test may be compromised.

4. Are blood test results are presumed to be valid?

Under California law, there is a presumption that blood-alcohol results were properly obtained. This means the burden is on the defense to establish that Title 17 procedures were NOT complied with.13

But even when Title 17 procedures are not complied with, a blood draw is not necessarily invalid. It all depends on whether a defendant's constitutional rights were violated.14

Example: Carl is pulled over for a broken taillight. The officer smells alcohol on his breath and asks Carl to take a Preliminary Alcohol Screening (“PAS”) breath test. Carl agrees and blows a .09%. The officer arrests him for Vehicle Code 23152(b), driving with a BAC of .08% or higher.

After his arrest, Carl elects to take a blood test to determine his BAC officially.15 Carl's blood is drawn by a medical assistant. The test results show a BAC of .10%.

But medical assistants are not authorized by law to do DUI blood draws. So Carl's criminal defense lawyer brings a motion to suppress evidence (California Penal Code 1538.5).16 The basis is that the Title 17 error constituted an violation of California's search and seizure laws.

But the court finds that the assistant was trained to do blood draws and had done over 100 of them. The procedures she followed were ones set forth in Title 17.

As a result, even though the regulations were not followed, Carl's constitutional rights were not violated. His arrest is deemed valid.17

california dui and blood test blood sample
In California, DUI blood draws must be done with the driver's consent or with a warrant.

5. Can police force a person to take a blood test?

5.1. Warrantless draws

With few exceptions, the police cannot take blood from a suspected DUI driver against the driver's will unless they have a warrant. This is true even if the police reasonably suspect the driver of drug use.

This is because of a United States Supreme Court case called Birchfield v. North Dakota.18 In Birchfield, the court held that the Fourth Amendment permits warrantless breath tests after a drunk driving arrest, but not warrantless blood tests.

But like most U.S. Supreme Court cases, the Birchfield case was narrowly decided. Its holding applies only to laws that make it a crime for someone to refuse a blood test after a drunk driving arrest.

California does not make chemical test refusals a crime

California law does not make it a crime to refuse to take a DUI blood test. The only penalties for a chemical test refusal in California are:

So it remains for California courts to decide if these penalties are unconstitutional after Birchfield.

And note that a warrantless breath test does not violate a driver's constitutional rights.

5.2. Blood tests with a warrant (forced blood draws)

With a warrant, an officer can physically force a driver to submit to a DUI blood test. An officer may seek a warrant if he/she believes a drunk or drugged driver caused an accident.

In this situation, the driver will be taken to a nearby hospital or medical facility. If necessary, the driver will be restrained by as many officers as it takes so that a lab technician can draw his or her blood.

The police may also get a warrant for a blood draw if a driver is unconscious or deceased.

6. Can a driver have blood tested in an independent laboratory?

California's DUI blood testing laws require that some of the driver's blood be saved for independent testing. This is one major advantage blood testing has over a breath test.

With a breath test, the results are instant. No portion of the sample is saved.19

But Title 17 requires the police to retain a portion of the driver's blood for one year after collection.20 (If the driver was deceased this period is reduced to 90 days).21 The police lab must then make it available to the driver if the driver wishes to have it independently retested.22

To exercise this right, the driver's DUI defense attorney will file a California “blood split motion.” This allows the lawyer to have the blood independently and confidentially analyzed by a private laboratory of the driver's choosing.

An independent lab might conclude that the sample:

  • Showed a BAC of less than .08%,
  • Had fermented or been contaminated,
  • Was improperly refrigerated or handled, or
  • Was otherwise affected in a way that might cast doubt onto the police lab's conclusions.

7. How can the results be challenged in court?

Experienced California DUI defense lawyers have three main strategies for challenging DUI blood test results:

  • File a motion to exclude the test results from evidence, or
  • Aggressively attack law enforcement's conclusions in an effort to get a DUI plea bargain or a "not guilty" verdict at jury trial.

A lawyer will pursue one or both of these strategies along with other DUI defenses such as:

And if the driver was the victim of a forced blood draw, a skilled DUI defense attorney will be extra vigilant. As well-known Barstow DUI defense attorney Michael Scafiddi23 explains:

"It's very likely that a rushed or otherwise unexpected blood draw could involve bad protocol. These are mistakes that could ultimately vindicate my wrongfully accused client."

Charged with DUI in California? Call us for help…

California dui and blood test dui attorneys
Call us at (855) LAW-FIRM

If you took a blood test after you were arrested for driving under the influence in California, our DUI defense lawyers may be able to help.

Call us at 855-LAWFIRM to speak to an experienced California DUI defense attorney in your area.

We have local offices in Los Angeles, the San Fernando Valley, Pasadena, Long Beach, Orange County, Ventura, San Bernardino, Rancho Cucamonga, Riverside, San Diego, Sacramento, Oakland, San Francisco, San Jose and throughout California.

The lawyers in our Las Vegas and Reno law offices fight the results of blood tests in Nevada DUI cases.


Legal Resources:

  1. See, in particular, 17 California Code of Regulations (“CCR”) 1219.1.

  2. California Vehicle Code 23612(a) (1) VC

  3. Vehicle Code 23612 (a)(2)(B)

  4. Vehicle Code 23612 (a)(2)(C)

  5. Vehicle Code 23612(a)(5)

  6. Vehicle Code 23612(a)(3)

  7. But some studies have found that the greatest predictor of accuracy is how soon after an arrest a test is given. See, e.g., Roiu, Birngruber, Spencer, Wollersen, Dettmeyer and, Verhoff, “A comparison of breath- and blood-alcohol test results from real-life policing situations: a one-year study of data from the Central Hessian police district in Germany,” and Gainsford, Fernando, Lea, and Stowell, “A large-scale study of the relationship between blood and breath alcohol concentrations in New Zealand drinking drivers.”

  8. 17 CCR 1219.1(a).

  9. 17 CCR 1219.1(b).

  10. 17 CCR 1219.1(d)(2)

  11. 17 CCR 1219.1(c).

  12. 17 CCR 1219.

  13. See, e.g., Davenport v. Department of Motor Vehicles (1992) 6 Cal. App. 4th 133. (holding that drivers bear the burden of proving a failure to comply with applicable statutory and regulatory requirements in California DMV DUI license suspension hearings.)

  14. People v. Esayian (2003) 5 Cal. Rptr. 3d 542. (“Clearly a blood draw is a medical procedure and must be conducted in keeping with medical requirements for such procedure. The Vehicle Code creates a statutory scheme for such draws, but noncompliance with the statute does not, by itself, demonstrate the methods used were improper.”)

  15. See Vehicle Code 23612(a) (1) VC, California's “implied consent” law. This law requires drivers to submit to a breath or blood test to test their blood alcohol content if they are lawfully arrested for driving under the influence.

  16. See Schmerber v. California (1966) 384 U.S. 757, 86 S.Ct. 1826, 16 L.Ed.2d 908.

    See also People v. McKay (2002) 27 Cal.4th 601, 117 Cal.Rptr.2d 236, 41 P.3d 59 (holding that violation of a statute does not render an arrest unreasonable within the Fourth Amendment and that such statutory violations cannot serve as the basis for the application of the exclusionary rule.)

    See also People v. Ford (1992) 4 Cal.App.4th 32, 5 Cal.Rptr.2d 189 (holding that the taking of blood without informed consent does not compel exclusion of the blood test results unless the manner in which the sample was obtained rendered the procedure constitutionally impermissible.

  17. Facts based on People v. Esayian, endnote 14.

  18. Birchfield v. North Dakota (2016) 579 U.S. ____, 136 S.Ct. 2160.

  19. See California v. Trombetta (1984) 467 U.S. 479 (holding that failure to retain breath samples after a DUI breath test does not violate a defendant's constitutional due process rights). See our article on Trombetta Motions.

  20. 17 CCR 1219.1(f).

  21. 17 CCR 1219.1(f)(1).

  22. 17 CCR 1219.1(f)(2).

  23. Barstow DUI defense attorney Michael Scafiddi is a former police officer who uses his inside knowledge of police procedure to defend clients accused of DUI and driving offense in courts and DMV hearing offices throughout San Bernardino, Riverside, Los Angeles, Orange, and Ventura counties.

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