The Truth About Chemical Testing in a California DUI Investigation

Drivers who are pulled over and placed under arrest for driving under the influence will likely be required to submit to one or more chemical tests. These tests are designed to detect whether the driver has alcohol or drugs in their systems and in what quantity. The results of these chemical tests often form the backbone of a prosecutor’s case against a driver. For example, a chemical test showing a driver’ breath- or blood-alcohol concentration to be greater than .08 may be the central piece of evidence a prosecutor relies on in pursuing charges against a motorist.

Prosecutors and police officers alike want drivers and jurors to believe these chemical tests are “scientific” and “foolproof.” The truth about chemical testing in California, though, is more complicated.

Breath Tests

Breath testing on a breathalyzer machine, such as the “Intoxilyzer,” is by far the most common chemical testing requested because the testing process itself is relatively quick to perform and because it does not require someone with medical knowledge or training to assist in collecting the sample. In a breath test, the driver blows into a tube connected to the testing machine. The machine collects a sample of the person’s breath and then analyzes that sample using infrared energy and approximates the person’s alcohol concentration.

This breathalyzer chemical test is not to be confused with the roadside breathalyzer, or “Preliminary Alcohol Screening” (PAS) test that officers use when they suspect a driver is intoxicated. In California, a chemical test is required, but only after a person has been lawfully arrested on suspicion of driving under the influence. The roadside breathalyzer is not a “chemical test” in that it is not required, and considered a “field sobriety test,” which are optional.

Blood Tests

A blood test is another chemical test that may be performed during a DUI investigation. Blood tests are often considered the most reliable of the three types of chemical tests. A blood sample is drawn from the driver and is then sealed and delivered to a laboratory. At that facility, a forensic scientist analyzes the blood sample using specialized equipment to determine the alcohol concentration in the person’s blood. Despite the testing and analysis occurring in a laboratory facility, there are still opportunities for errors to occur that might render the results unreliable. Samples of blood that are not packaged properly, that are drawn too long after officers see the driver operating their car, or that are tested using defective equipment may all provide inaccurate blood alcohol content results.

Urine Tests

Urine tests are considered the least reliable of all of the chemical tests and are usually reserved for cases where the driver is suspected of being under the influence. The machines used to evaluate the urine of DUI suspects, for example, often confuses the chemical compounds of different drugs, cannot tell when the drugs were used, nor can it tell how intoxicated someone is. Fortunately, urine tests, by law, are not to be used in California as a chemical test unless both a breath test and a blood test are unavailable, which in most jurisdictions, is highly unlikely.

Which Chemical Test Should a California Driver Take?

According to California Vehicle Code 23612(a)(2)(A), drivers who are lawfully arrested on suspicion of having driven under the influence of alcohol are to be informed by the officer that the driver may choose whether to submit to a breath test or a blood test. The driver’s choice is to be honored unless the driver is unable to complete their chosen test. As stated above, only if both a breath test and a blood test are unavailable should a urine test be used.

Refusing to submit to any chemical test can have serious and negative consequences for a person’s driving privileges. Choosing to take a breath or a blood test should be made after considering the facts of the situation. While blood tests are generally more reliable, they may also be able to detect the presence of drugs in the driver’s system. Thus, if someone consumed any drugs but little or no alcohol, it may be better for them to request a breath test be performed. In addition, those laboratories who perform testing on a driver’s blood sample must preserve a sufficient amount of the sample so that the driver may obtain an independent analysis of the sample. This is known as a “blood split,” and the driver obtains the sample for independent testing through a court order.

Breath testing does not provide a driver with a sample that can be independently tested, but the problems associated with breath testing machines tend to be more significant and numerous. Thus, if a person believes they are close to or under the legal limit, a breath test result may be easier to challenge in court.

Chemical Testing is Not Dispositive in a California DUI Case

Even though law enforcement officers and prosecutors would have drivers believe otherwise, the results of a chemical test – whether a breath, blood, or urine test – are not beyond questioning. In fact, the quality of any chemical test result depends on a myriad of factors, including:

  • Whether the sample was timely collected and collected in a safe and careful manner;
  • Whether steps were taken to prevent contamination of the sample;
  • Whether the sample was appropriately stored prior to testing;
  • Whether the person analyzing the sample was adequately trained on the testing equipment and protocols;
  • Whether the testing equipment was working properly or if there were unaddressed errors in the machinery’s code or parts
  • Whether a proper observation period (if applicable) was observed to ensure the person did not belch, vomit, or put anything in their mouth before giving a breath sample

A California defense attorney with experience defending drivers from drunk driving charges can examine the facts of a particular DUI investigation and know how best to attack the chemical testing results. Samples that were collected after an unlawful arrest, that were not collected in accordance with protocols, or that were not appropriately analyzed may all be subject to suppression.

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