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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 breath test. It is subject to a variety of errors and challenging the result and accuracy of a breath test is a defense strategy that can be employed in fighting against DUI cases.

What is a breath test?

A breath test is usually taken with a “breathalyzer”. A breathalyzer is a machine that measures the alcohol from the deepest part of a person’s lungs instead of the blood. The breathalyzer then converts the reading to an approximate equivalent in blood alcohol percentage. In California, BAC is measured by grams of alcohol per 100 milliliters of blood or grams of alcohol per 210 liters of breath.[1]

California law requires that breath samples must be essentially alveolar in composition.[2] The reason for this is because alcohol can only be found from the deep portion of your lungs, from the alveoli, so the air from this part of the lungs is more commonly known as “deep lung air”. To get an accurate reading, you need to blow into the breath testing device hard enough to get to the deep lung air. The problem with this test is that not everyone can breathe out on the testing device hard enough to get an accurate reading, particularly older people and those with medical conditions.

When is a breath 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.

  1. Preliminary Alcohol Screening Test (PAS Test)

A preliminary alcohol screening or PAS test is usually conducted after a traffic stop but at which point, no arrest has been made yet. This test is specifically conducted by the arresting officer when they suspect that a driver might be under the influence. A driver may lawfully decline to take this test. However, there are certain drivers that may not decline and have to comply, particularly: 1) drivers under the age of 21; and 2) drivers on probation for a prior DUI.

  1. Post-arrest Test

A post-arrest test is conducted after a driver has been lawfully arrested for a DUI. The results of this test can be used in court as evidence. A driver arrested for DUI will be required to take a chemical test (choice of a breath test or blood test). 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

Most people wonder if opting for one test is better than the other. There is no consensus amongst DUI lawyers regarding which test is better to take. But what is clear is that they both have their own pros and cons.

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.

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.

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 conducting and processing breath tests but also with regard to the training of persons conducting the tests, maintaining and calibrating the testing devices.

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

  • The breath testing device must be kept in good working order and the device must be calibrated every 10 days or after 150 uses,[3] whichever comes first.
  • The law also requires that the driver must be observed continuously for 15 minutes before the breath test is given. During those 15 minutes, the driver must not be smoking, eating, drinking, or have anything in their mouth, burp, regurgitate, or vomit.[4] The reason is this can affect the breath test results if the driver had anything in their mouth immediately prior to the test.
  • When taking the breath sample, two breath samples must be obtained that do not differ by more than 0.02 grams per 0.1 liter of blood alcohol.[5] This means that you may have to blow into the breath testing device more than two times.
  • The laboratory performing the analysis must keep detailed records of equipment calibration, personnel, and test results, among others.

Without following these regulations, the test results can be affected leading to inaccuracies like higher BAC readings. An experienced California DUI defense lawyer will not only look into the accuracy of the BAC itself but also verify if all the laws and procedures were followed regarding the breath test.

Possible Defenses

Below are some possible defenses against breath 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:

  • Rising blood alcohol level – this means that when the driver got inside the vehicle, his or her BAC level was still within the legal limit but due to the passing of time, the alcohol is absorbed by the body. It can be argued that the BAC was still rising when the test was conducted
  • Existing medical condition/medication being taken – Some medical conditions and medication can produce gas and acids in the lungs and stomach that can be read by breath testing devices the same way as alcohol from an intoxicating beverage. This can lead to false BAC readings, therefore, it is best to disclose to your defense attorney any existing medical condition or medication that you might be taking at the time of your arrest as this could have affected the BAC results.
  • Residual mouth alcohol – sometimes an alcoholic beverage leaves traces in the mouth. Because of the manner of how breath tests are taken, this can sometimes fool breath test devices into providing results that read as falsely high BAC readings.
  • Failure to follow Title 17 protocols – as stated above, the protocols on breath tests and blood testing must be followed by law enforcement agencies because the non-calibration of equipment, or a driver that was allowed to chew gum within 15 minutes prior to a breath test, might have a falsely high BAC reading, among other scenarios.

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) 827-7222for the representation you need.


[1] Supra note 1.

[2] 17 California Code of Regulations §1215 (r)

[3] 17 California Code of Regulations § 1221.2 (a) (2) (B).

[4] 17 California Code of Regulations § 1221.1 (b) (1)

[5] 17 California Code of Regulations § 1221.2 (a) (1)

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