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DUI: Breathalyzer v. Blood Test:

San Bernardino DUI Attorney & Redlands DUI Attorney

In most DUI cases the evidence will include the results of a Blood Alcohol Content test (BAC). Note: If the defendant refuses to take a BAC test he or she will automatically lose his or her license for at least a year. This is a review of the different B.A.C. tests:


DUI Breathalyzers are the most common type of devices used to measure BAC. There are two different types of breathalyzers: The Preliminary Alcohol Screening (PAS) device which is a small portable device which measures the amount of alcohol on the driver’s breath. This machine is supposed to measure the BAC but the machines are fairly inaccurate and must be regularly calibrated and maintained by law. The machines are subject to human error by way of improper administration of the test by the officer and the machines do not take into consideration the recent drinking pattern of the driver or the metabolism of the driver. The P.A.S. device is an on-site device which is only used to help the officer establish probable cause to believe the driver is DUI.

The second breathalyzer test is the non-portable device which is located at the police station. This is not a P.A.S. device and is considerably larger in size and also considered to be more accurate. The problem with the results of this test is that the sample is sometimes stale or old because it is taken too long after the DUI arrest itself. The fact that a driver has a high BAC at the time the sample is taken at the jail is not generally an accurate measurement of what the driver's BAC was when he or she was driving.  The breathalyzer may be used in court and at DMV hearings as evidence to establish the driver's BAC. However, there are many arguments that can be made on behalf of the defendant which dispute the reliability of the breathalyzer results, such as human error in administering the breath test, improper calibration or maintenance of the breathalyzer equipment, and timing of the taking of the breath samples (the samples are often times taken long after the driver was observed driving).

Blood Samples:

The DUI blood test is generally the most accurate of the different tests; however, this does not mean that blood tests are full-proof or that they are 100% accurate. Common errors do occur.

For example: the vile of blood sample is partially filled with preservatives and anti-coagulants. If the lab-tech does not mix together the proper amount of these foreign chemicals the blood tends to ferment (produce its own alcohol). The fermentation of the blood leads to a higher, but artificially false, BAC result. Only independent testing of the blood could reveal a contrary BAC.

Another example of improper handling of the blood which leads to fermentation is improper refrigeration. Sometimes the handlers of the blood inexcusably delay proper refrigeration of the evidence.

Furthermore, blood sampling can only be accomplished by a certified lab-tech. It might come as a surprise that an increasing number of lab-techs are not properly certified to handle blood. Where this is the case, the credibility of the blood results is diminished substantially. Lab-techs are supposed to be trained on how to take samples of blood so as not to create false positives of the presence of alcohol. For example, if the lab-tech uses an alcohol-based antibiotic to clean the skin at the area where he or she draws the blood then the blood results could be flawed due to the presence of the alcohol-based antibiotic cleanser mixing with the blood sample.

It is also important to remember that a DUI blood test only shows what the BAC was at the time the test was performed. If the blood test is performed long after a person is arrested for DUI, then it is possible for the BAC levels to have risen from the time of arrest to the time that the blood is tested.

It is also important to remember that a person can be forced to take a blood test on an arrest for DUI; therefore, the defendant should submit to the test .

Finally, the results of the DUI blood test are not presumed to be accurate where the test was taken more than three hours after the arrest for the DUI.

A San Bernardino DUI Attorney will review the blood results in a DUI case in search of errors made by the lab-tech or the arresting officer. Both the lab-tech and the arresting officers are required to take certain steps to ensure accuracy of the results of a DUI blood test. These requirements are listed at Title 17 of the California Code of Regulations.

Scientific evidence of a high BAC after a DUI arrest is generally strong evidence but it is not fatal to a case. Sometimes the DUI evidence is subject to wild inaccuracies due to human error, mechanical error, procedural error, or factual circumstance.

Lastly, remember that it does not matter what the driver’s BAC is if the officer did not have a valid reason for stopping the driver in the first place. Officer must have probable cause to believe the driver is DUI before any arrest is made. Besides the P.A.S. test, breathalyzers and blood tests are taken only AFTER a driver is arrested. Therefore, if the arresting officer did not arrest with probable cause, all of the BAC evidence must be excluded.

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