DUI Chemical Tests


An important element of proving the offense of driving under the influence (DUI) is the blood alcohol content (BAC) present at the time of your arrest. While roadside sobriety tests often are administered by the police to determine impairment, chemical testing in the form of breath and blood tests are more reliable for ascertaining BAC levels. Nevertheless, the results of a San Diego BAC test, as well as the procedure used, can be riddled with errors, inaccuracies, and problems. A drunk driving attorney can help you understand DUI chemical tests. Contact us online or call us today to learn how we can defend your rights.

Breath Testing

The majority of DUI cases in California are based on the results of one of two types of breath tests. A preliminary breath test is generally administered by the police after you’re pulled over. The officer uses a handheld device and this is normally done before the driver is arrested. Generally, after an arrest, a further test using a desktop breathalyzer is done at the police station. Preliminary breath tests cannot be used as evidence of your DUI, but can be used as probable cause for your arrest. The desktop breathalyzer test is the one that can be used as evidence of your guilt in your DUI case.

A roadside breath test prior to arrest is optional. The law allows refusal unless you are under 21 years of age or you are currently on probation for a previous DUI. However, once you are under arrest, you are required by law to submit to chemical testing and any refusal will result in an administrative suspension of your driver’s licensed and may be used in California to enhance the penalties if you are found guilty of your DUI charge.

It is important to know that there are established procedures that the police must use when administering a breath test in a DUI-related case. Such rules include:

  • Using only approved devices
  • Breath testing devices must be calibrated and tested on a regular basis
  • Police officers are to be trained in the use and administering of the breath device
  • An observation period of 15 minutes prior to administering the breath test must be followed
  • There must be proper records relating to the calibration of the device, the arrest, and the test results

Any breach of these or other procedures can form the basis for a sound defense should your DUI case goes to trial.

Breath test machines can be unreliable, and there are errors that can lead to false readings. Such errors can include:

  • Improper calibration
  • Police error
  • Medical conditions of the person being tested
  • Contamination of the sample
  • Poor record keeping

Blood Testing

A blood test is considered a more reliable form of testing to determine the BAC levels in a driver arrested for DUI. The test is administered after arrest and, compared to a breathalyzer, a blood sample is retained for possible independent testing by the defense.

Similar to a breath test, if you are arrested for DUI, refusing a blood test may significantly affect sentencing if you are later found guilty of the DUI. That being said, even the results of a blood test can be contested. Mistakes such as contamination, intermingling, and fermentation can all produce unreliable results. Like the breath tests, there are established procedures that must be followed to prevent such mistakes from happening.

If you are innocent, having an experienced DUI attorney is the key to fighting the results of a San Diego BAC test. It is important to keep a mental record of everything that transpired from the moment you were pulled over by the police and when you were released on bail. This information will be helpful to your lawyer.

Urine Tests

While breath and blood tests are the preferred BAC tests used by the police, a urine test is another San Diego BAC test that is sometimes utilized. Since 1999, urine tests are only administered under the following circumstances:

  • The police have suspicion that you are under the influence of drugs
  • Neither blood or breath testing is available
  • You are a hemophiliac
  • You are using anticoagulant medication

Urine tests are not considered to be reliable, and accordingly the law makes it the last resort for testing an individual’s BAC levels for a DUI arrest.

Hire An Experienced DUI Attorney to Challenge Your San Diego BAC Test

Chemical testing is an important aspect of all DUI cases. You will need the experience and knowledge of the legal defense team at McElfresh Law to challenge the results of chemical testing at trial. For years, we have represented individuals charged with all sorts of criminal offenses and you can trust our ability to fight for your rights and secure your freedom.

Call us today at (858) 756-7107 and let us be your DUI attorney of choice.