Posted by Phillip Crawford | Nov 13, 2020

Should I take a breath test or a blood test?

Always remember the Golden Rule for Staying Out of Jail:  DO NOT TALK TO THE POLICE.  Be polite and respectful.  Hand them your license, registration, and proof of insurance.  But do not answer ANY question asked by the police.  Period.  If the police ask if you know what day it is, politely but firmly say: “Officer, my lawyer told me not to answer any questions.”

If you are stopped by the police, and you are not on probation for a prior DUI conviction, or other crime requiring you to submit to field sobriety testing, you are not required to submit to any pre-arrest testing.  You are not required to perform the field sobriety tests and it probably won't help you if you do.  The tests are designed for failure.  (Read more here)  We have spoken to countless people who thought they performed well on the field sobriety tests but got arrested anyway.

Unless you are under 21, on DUI probation, or under arrest, you are not required to submit to a pre-arrest breath test.  The police will ask you if you are willing to take a “preliminary alcohol screening test.”  They are supposed to inform you that it is voluntary.  They may try to entice you into taking the breath test by implying that they will let you go if you blow under a 0.08% blood alcohol content. You are not required to take the test and taking the test is unlikely to help you.  In fact, even if the breath test shows you have no alcohol in your system, the police may still arrest you on the theory that you must be under the influence of a drug.

Unless you are under 21 or on DUI probation, the only time you are required to submit to a test is AFTER you've been placed under arrest for suspicion of driving under the influence.  At that point, the police should inform you that you must take a breath test or a blood test or you will lose your license for at least one year.  (If the police suspect you are driving under the influence of something other than alcohol, you will be required to take the blood test.)

When faced with the choice of taking either the breath test or the blood test, the safest option is usually the blood test, if you want to avoid a DUI conviction. 


  1. If you choose the breath test, you will be required to blow into the machine at least twice. Your blood will only be tested once.  It is easier for your attorney to challenge the accuracy of one test rather than two.
  2. If you are charged with violating Vehicle Code Section 23152(b), the prosecutor's job will be to prove that your blood alcohol content was 0.08% or higher at the time you drove your vehicle. Your blood alcohol level changes over time.  It rises for a while after drinking and then it goes back down.   It usually takes longer to have your blood drawn at the hospital than to have your breath tested at the police station.  And the more time that goes by between the time you drove and the time you take a test, the more difficult it becomes for the prosecutor to prove your alcohol level at the time you drove.
  3. The entire process of analyzing blood for alcohol is filled with possibilities for errors. The blood must be mixed with the proper amounts of preservative and anti-coagulant, refrigerated, protected from any contamination, and analyzed within a reasonable amount of time. Once the blood is drawn into a tube, it gets put in a police evidence locker.  At some point the blood tube gets transported to the crime lab in Watsonville and placed in a refrigerator.  At some point, a government technician will analyze a tiny portion of the blood for alcohol, using an incredibly complicated process called gas chromatography.  (For an overview of this process, read the attached article.)  Mistakes can happen anywhere along the line.  Some of these mistakes can change the amount of alcohol in your blood sample, leading to an unreliable test result. 
  4. In Monterey and Santa Cruz Counties, blood samples are analyzed at the Department of Justice crime lab in Watsonville. The lab uses a system called single column gas chromatography with a flame ionization detector.  This is an outdated and unreliable system.  There have been more reliable systems available for decades, including dual column gas chromatography and gas chromatography with mass spectrometry.  The Department of Justice knows they are using an outdated system.  In fact, they have already purchased a system using gas chromatography with mass spectrometry but haven't gotten around to installing it and training their technicians to operate it.  In the meantime, they continue to use this unreliable technology to prosecute and convict people for driving under the influence of alcohol. For an excellent article by attorney and forensic scientist Okorie Okorocha on the problems with single column gas chromatography, see: Mr. Okorocha's publication

To summarize, here are simple guidelines to follow if you don't want to be convicted of driving under the influence.

Don't drink and drive.  Although it is perfectly legal to drink and drive, as long as you have not had too much to drive safely, we've seen far too many people arrested and prosecuted who thought they were “okay to drive.” One drink is safer than two.  But zero is the safest amount.

Don't answer ANY questions asked by the police.

Unless you are under 21 or on probation for a DUI conviction, don't submit to any pre-arrest testing.  That means no field sobriety testing and no pre-arrest breath test.

If the police arrest you for suspicion of driving under the influence, choose to submit to a blood test.

As soon as you are released by the police, contact a qualified, experienced DUI trial attorney.   There are a lot of good attorneys out there.  Not all of them are good DUI attorneys.  Look for an attorney who is a member of the California DUI Lawyers Association and the National College for DUI Defense.  Look for an attorney who understands the science behind breath tests and blood tests.  Most importantly, look for an attorney who has a record of FIGHTING and WINNING DUI trials.  If you can find a firm with a better record of taking DUI cases to trial and winning NOT GUILTY verdicts, hire them.   We're confident you won't find other attorneys anywhere on the Central Coast who can match the record of the Crawford Law Firm.

About the Author

Phillip Crawford

Phillip Crawford is an award-winning DUI attorney. In 2018, he won the California DUI Lawyer's Association's top honor when he received the President's Award for excellence in DUI defense. His sole focus is defending DUI cases. Phillip is regarded by judges, prosecutors and fellow defense attorneys as the top DUI in the area who fights passionately for his clients.

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The Crawford Law Firm has been committed to its clients for over fourteen years. With offices in Monterey, Santa Cruz, and Salinas, CA, our focus is DUI and criminal cases in Monterey, Santa Cruz, San Luis Obispo, and Santa Barbara counties.

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