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Challenging Blood Tests in DUI Cases

One of the methods in determining blood alcohol concentration (also known as “BAC”) in DUI cases is by way of blood test. It is subject to a variety of errors and challenging the result and accuracy of blood tests is a defense strategy that can be employed in fighting against DUI cases.

When is a blood test taken?

In DUI cases, the law enforcement agency will measure the BAC at two different points: 1) prior to the arrest called “preliminary alcohol screening” (otherwise known as PAS test), and 2) after an arrest has been made.

After an arrest has been made, the arrested driver is made to take a chemical test and must be given a choice between a breath test or a blood test. This means a blood test can only be had after a legal arrest has been made and after the arrested person has given their consent to the blood testing (except in cases where a warrant was validly obtained for a blood draw). There is no blood testing during the PAS test.

The results of a test taken after arrest are usually used in court as evidence. Take note that refusing to take the chemical test at this point will have major consequences which include:

  • increased penalties on top of standard DUI penalties
  • a mandatory driver’s license suspension (regardless of the outcome of the DUI case)
  • can be used as evidence for admission of guilt

Breath Test vs. Blood Test

With a blood test, the law enforcement agency or authorized personnel who are in possession of the blood sample are required to store and preserve the remaining blood sample because the arrested driver has the right to have an independent laboratory conduct testing on the remaining blood sample. Compared to a blood test, the downside of a breath test is that you cannot have an independent laboratory conduct testing on a breath sample because there is yet no way to preserve breath samples taken during the breath test.

A breath test is non-invasive as you only need to exhale deeply from your mouth to the breath testing device. A blood test is invasive and will require the use of a needle and syringe to able to collect your blood sample. If you have a breathing problem, getting an accurate reading may be difficult, as mentioned earlier.

For breath tests, the results are immediately available, provided that you were able to give a viable deep-lung breath sample. The blood test on the other hand could take a long time, sometimes months after the test, before the results are available.

Choosing between which test to take will depend on the circumstances but each test has its pros and cons.

Title 17 of the California Code of Regulations

This law sets forth the rules and protocols that must be followed concerning breath and blood tests. Accordingly, law enforcement agencies are required to follow strict protocol not only when collecting and processing blood samples, but also a trained technician or medical professional shall be the one to collect the blood sample.[1]

Some of the more important protocols to keep in mind are as follows:

  • The area where blood will be drawn from cannot be sterilized by an alcohol-based product[2]
  • A sufficient amount of anticoagulant and preservative must be added to the blood sample to preserve the sample and prevent contamination or clotting[3]
  • Testing equipment cannot be cleaned or kept in alcohol or other volatile organic solvents[4] as this could also have an effect on the blood sample taken
  • Chain-of-custody should be properly followed, recorded, and maintained[5]

Blood test results enjoy the presumption of regularity. This means that the courts will presume that law enforcement agency, lab technicians, or medical professionals involved in the blood testing properly did their jobs and that the blood sample was obtained according to the law. It is up to the defendant to show that the procedures were not followed properly. An experienced California DUI defense lawyer will not only look into the accuracy of the BAC results itself, but also verify if all the laws and procedures were followed regarding the conduct of the blood test and the preservation of the blood sample. Conducting an independent blood test (the remaining blood sample can be obtained via a “blood split motion”) can help in showing if any procedures or protocols were not followed.

Possible Defenses

Below are some possible defenses against blood test results. However, defenses against DUI charges are not limited to what is listed below and will mostly depend on the circumstances of each case:

  • The law enforcement agency had no probable cause to conduct a traffic stop which lead to the DUI arrest
  • Rising blood alcohol (the blood was drawn during a time when the body was still absorbing the alcohol leading to higher BAC results)
  • The blood was drawn without the consent of the arrested driver (post-arrest testing)
  • Independent test conducted on the blood sample shows a different result from the test conducted by the law enforcement agency

No Judgment, Only Professionalism

If you have been arrested or charged with a DUI, it is all-important to hire an experienced, aggressive, and seasoned private West Covina defense lawyer to fight your case. We always make our clients feel right at home and we encourage you to take comfort in the fact that you have a dedicated advocate on your side at Coimbra Law Firm, APC. Our highly-experienced lawyers at Coimbra Law Firm, APC will help ensure that your Constitutional rights are protected. Each of our clients will receive personalized attention, complete discretion, and trained staff working to provide the best legal assistance available.

Our only job is to defend you with the maximum competence, diligence, and zealousness. Do not hesitate to call us at (626) 827-7222 for the representation you need.


[1] 17 Code of California Regulations §1219.1 (a)

[2] 17 Code of California Regulations §1219.1 (b)

[3] 17 Code of California Regulations §1219.1 (d) (2)

[4] 17 Code of California Regulations §1219.1 (c).

[5] 17 Code of California Regulations §1219

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