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Blood Alcohol Testing

Blood alcohol testing allows law enforcement to determine how much ethyl alcohol is in a person’s bloodstream. The results are given in percentage in milligrams. If someone has a blood alcohol test result of 0.08% or higher, he or she is considered impaired according to California DUI law. If a person’s blood alcohol test result is slightly below 0.08%, he or she still might be considered under the influence of alcohol if he or she displays certain behavior.

It is important to remember that the blood alcohol test is intended to determine the driver’s blood alcohol concentration at the time the he or she was operating a motor vehicle, and not after the fact. There can be a significant difference between a driver’s BAC at the time of driving and the time the chemical test is administered. California law requires evidential blood tests to be conducted in compliance with California Code of Regulations. Title 17 is the governing section of the California Code of Regulations applicable to blood alcohol testing.

There are three types of tests that law enforcement uses to determine a person’s blood alcohol level. Blood alcohol can be measured by a person’s breath, blood, or urine. Certain factors such as gender, amount of alcohol consumed, weight, type of alcohol consumed, and food consumption can significantly impact the results of a blood alcohol test.

Breath Alcohol Testing

During a breath alcohol test, the person blows into a machine such as an Intoxilyzer 5000 manufactured by CMI. A person’s breath alcohol concentration is indirectly correlated to a person's blood alcohol level. However, the formula chosen by the California State Legislature to establish the relationship between breath alcohol results and blood alcohol level is arbitrary and does not apply to each individual. The American Medical Association has reported that a person may be impaired with a BAC of 0.05%. Most states, including California, have adopted 0.08% as the standard. This means there is 0.08 grams of alcohol present per 210 liters of breath.

Blood Alcohol Testing

Through a blood alcohol test, a person’s blood alcohol content can be directly determined. Blood testing is the most accurate way to determine a person’s blood alcohol concentration at the time of the chemical test, not necessarily at the time of driving. During a blood alcohol test, blood is drawn from a person’s arm, and then it is analyzed. If the blood test reveals the person’s blood alcohol concentration to be 0.08% or greater, that person is considered impaired.

Often there is a delay in the specialist (phlebotomist) who draws the blood responding to the law enforcement facility to obtain the sample. This can leave the blood alcohol result open to challenge because the blood alcohol level may have risen since the time of driving.

Urine Alcohol Testing

A urine alcohol test measures a person’s blood alcohol concentration indirectly. After a urine sample is obtained, it is analyzed, and a ratio of 1.3:1 is used in estimating the alcohol concentration in the urine. If the urine test reveals that the person’s blood alcohol concentration was 0.08% or greater, he or she is considered impaired. The problem with urine testing is that unless there was a complete void (emptying) of the bladder prior to obtaining a sample, the results are subject to challenge because urine may remain in the bladder for a prolonged period of time.

DUI Blood Testing or Blood Alcohol Analysis involves the collection, storage and analysis of blod drawn following an arrest for driving under the influence. Collection of blood from a person suspected of driving under the influence. In California the blood must be drawn in a medically approved manner. The person who draws the blood must be either a nurse or a licensed phlebotomist.

Collection of the Blood Sample

The manner in which the blood sample is collected, or drawn can affect the integrity of the blood sample. Errors associated with the blood draw can lead to inaccurate results or even false positive analysis. This is because the drawing of blood to be used as evidence in a DUI criminal prosecution is a sensitive medical procedure. Compounding the risk of reporting errors, most individuals performing the blood draws have limited background or training in the medical field.

Despite wearing a lab coat most phlebotomists have completed a program of study consisting of no more than a 40-hour training course and 40 hours on the job training without any real understanding of the significant medical and legal aspects of drawing blood. As a result of this minimal training the integrity of the specimen is often compromised.

Storage of the Blood Sample

The conditions in which the blood sample is stored and maintained prior to being analyzed may be a further source of error leading to inaccurate and false positive results. Studies have shown error rates well over 100% can result from delays and improper storage of blood specimens. All the conditions required for fermentation (creation of alcohol) are present within the blood test vial. This includes the presence of yeast, sugar and bacteria which may exist in a person's whose blood is drawn.

Even short delays or changes in temperature can create the conditions leading to fermentation. As a result of fermentation the amount of alcohol in the blood vial where the specimen is held will increase so that the total amount of alcohol in the blood specimen may be higher than what was existed in the person’s body at the time the blood was drawn.

Testing of the Blood Sample

Most forensic labs involved in analyzing blood specimens for alcohol on behalf of law enforcement use a procedure involving a machine known as a Gas Chromatograph. Often times the manner in which this equipment is employed results in a presumptive determination of alcohol as opposed to a confirmatory method specific to alcohol. This method can cause compounds which may respond to the method of detection in a manner similar to alcohol to be falsely measured as alcohol. Additionally, this method cannot determine whether the alcohol being measured was originally present in the person’s body or whether the alcohol being measured is that formed during any delay before analysis was performed.

San Francisco DUI Attorney

If you have been arrested for DUI anywhere in the San Francisco Bay Area, obtaining a qualified attorney is the most important decision you will make. An experienced and committed DUI defense attorney can protect your legal rights, investigate the circumstances surrounding your arrest, question law enforcement officers and independent witnesses, and inform you of your options, . A skilled DUI attorney can also provide the resources and aggressive defense you will need to successfully fight your DUI charges in order to win your case or minimize the impact.

Robert Tayac has been helping people charged with DUI in San Francisco for over twenty years. He has the education, specialized training, and experience to help you and manage or defend your drunk driving case. Robert Tayac will also schedule your hearing with the California DMV and represent you at the hearing. Remember, you only have 10 days to prevent your driver's license or privileged to drive from automatically being suspended by the DMV. If you hire Robert Tayac, you will know that you have retained the services of a knowledgeable and trustworthy DUI defense lawyer and that your case is being properly handled.

Office Location and Areas We Serve

The Law Office of Robert Tayac is located in downtown San Francisco at 505 Montgomery Street, 11th Floor San Francisco, California 94111. Satellite offices are maintained in Napa, Redwood City, San Rafael, and Walnut Creek. For more information on driving under the influence matters in neighboring cities and counties, feel free to review the county specific information on the resource pages listed below:

Contact The Office

Mr. Tayac and the DUI investigators and experts working with him stand ready to help you or your family member. A member of the office is available to speak with you regarding the case any day of the week between the hours of 8:00 a.m. and 8:00 p.m. Pacific Standard Time at 415-552-6000.

If you hire the Law Office of Robert Tayac, you will know that you have retained the services of the most knowledgeable and experienced DUI defense team.

Why Choose Our Firm?

Attorney Robert Tayac Puts a Long, Decorated Career to Work for You
  • Puts Over 20 Years of Experience Toward Your Case

  • Specialized Education in DUI Defense

  • Has Trained Other Attorneys in San Francisco

  • Former San Francisco Police Officer & Police Inspector

  • Certified by the SFPD on the Intoxilyzer 5000 Testing Device

  • Co-Authored the 4th Edition of California Drunk Driving Defense

  • Boasts a Successful Record Achieving the Best Result for His Clients

  • Takes the Time to Understand You & Your Case

Client Testimonials

  • “I did have to pay a fine and attend a 3 month school but I was able to maintain my license.”


  • “You made me feel confident and reassured that all aspects of my case were being handled in a professional and efficient manner.”


  • “He's professional, honors his promises, and gets excellent results for all his clients.”


  • “Don't go it alone - you will get a very different (better) result with Robert's lead.”


  • “His guidance through the whole process during a difficult and emotional time was such a support. I highly recommend him. He is simply the best DUI attorney.”

    Former Client

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