Breath & Blood DUI Test Defense in Ventura

There are two common types of tests that are used to determine alleged blood alcohol level in a DUI investigation: the breath test and the blood test. Both tests are subject to attack on a number of bases, ranging from operator error to the potential for sample contamination, to the limitations of the testing methods themselves.

If you believe your breath or blood test yielded a false positive, contact our office at (805) 669-9744 or complete our online contact form

How Does Law Enforcement Administer a Breath Test? 

When it comes to the breath test, there are three types of machines that are commonly in use: the Preliminary Alcohol Screening Test device, the Intoxilyzer 5000 used at the station, and the Alcosensor 4-XL with point of arrest system used in the field.

The Preliminary Alcohol Screening (PAS) Test device is used by officers in the field as part of their battery of observations, evaluations, and field sobriety tests given to detect excessive blood alcohol level or intoxication. 

The accuracy of results from the Preliminary Alcohol Screening Test is subject to attack on a number of bases, including: 

  • the officer’s failure to adequately maintain
  • calibrate and operate the machinery
  • the limitations inherent in the machine itself (such as the inability to detect mouth alcohol and interfering substances)

A further defect in the Preliminary Alcohol Screening Test device is the fact that it relies on the law enforcement officer to calibrate and maintain the device, unlike both the Intoxilyzer 5000 and the Alco Sensor 4XL, which rely on a scientist to maintain and calibrate the device. This fact of reliance on an individual law enforcement officer, often operating under time constraints, involves a range of potential problems from operator error to failure to follow specified protocols, to errors with maintenance and calibration of the device. All these potential pitfalls can be used to cast doubt on the validity of the Preliminary Alcohol Screening Test result.


  • “Attorney Zide always is professional, prompt and very knowledgeable. She truly cares about her clients' lives as well as their legal matters.”

We Can Help You Create a Strong Defense 

At the Law Office of Jennifer Zide, we aggressively challenge the validity of your test result. We seek information as to the officer’s training and experience in dealing with these machines, his or her actual operation of the machine in question, any history of errors or problems with the machine used in your case, and any other information which may be cast doubt on the reliability of the instruments or operators involved in evaluating your samples. We work with a forensic toxicology expert who has extensive experience in evaluating all the issues surrounding your test results. Our expert will analyze your case and help us expose the weaknesses in the prosecution’s case.

Throughout this entire process, from our initial meeting to discuss your case, to our meetings with our expert, you will be fully included. At the Law Office of Jennifer Zide, our Ventura lawyer will never lose sight of the fact that you are our client. We want you to be involved in our findings and our strategies, and to understand all the information at the heart of your defense.

For more information on the arguments that we can make as your Ventura defense attorney, call the Law Office of Jennifer Zide today at (805) 669-9744 or reach out using our online contact form to discuss the unique facts and circumstances in your case.

Intoxilyzer 5000 or Alco Sensor 4-XL with Point of Arrest System 

For your final Breath Test, you may be given a test either on an Intoxilyzer 5000 machine at the police station or in the field on an Alco Sensor 4-XL with point of arrest system. 

Both machines are open to attack on a number of bases, including:

  • potential operator error and failure to follow protocols which are in place to guarantee the validity of a sample
  • potential sample contamination
  • margin for error
  • the limitations of the machines themselves (including inability to detect interfering substances or mouth alcohol which may give a false reading)

Studies have shown that a wide range of substances which are volatile in a person’s blood can be falsely identified as alcohol by both the Preliminary Alcohol Screening Test device and the Alco Sensor 4-XL used in the field. Furthermore, any results that are obtained more than a certain range of each other should be viewed with suspicion. For machines to be judged “reliable” they must give results on one subject which are within a certain range of each other, specifically readings within .02% blood alcohol content. Readings that are out of keeping with that standard and or machines that offer disparate results will be seen as unreliable. Such disparate results will not be admissible in court under Title 17, a statute whose purpose is to make sure that only reliable evidence is allowed to be used against you.

How Does Law Enforcement Administer a Blood Test? 

As with the breath test, there may be a number of issues that could lead to a compromised blood test result in your case. 

These issues include: 

  • maintenance and preservation of the sample
  • sample contamination
  • potential errors in the blood draw itself

It is important to note that if a blood sample is not properly preserved, this error could lead to an inaccurate or falsely high reading. Also, because of the time gap involved between the point of driving and the point at which the sample is taken, there may be other issues involved. Factors such as the time gap and actual drinking pattern factor into any defense argument that the test “result” does not necessarily reflect blood alcohol level at time of driving.

Why Choose Us? 

  • Full Case Review by a Dedicated Toxicology Specialist With Over 30 Years of Experience
  • Private Investigator Available for Everything From Witness Statements to On-Site Investigations
  • Military & Student Discounts Available
  • We Keep You Fully Informed At All Times

Get in Touch

We Are Always on Your Side

  • Please enter your first name.
  • Please enter your last name.
  • Please enter your phone number.
    This isn't a valid phone number.
  • Please enter your email address.
    This isn't a valid email address.
  • Please make a selection.
  • Please enter a message.