Challenge Your Breath, Blood & Field Sobriety Test Results With a Top Vista Lawyer
During a California DUI stop, police rely on a series of tests to determine whether you’re driving under the influence. These include chemical tests that are mandatory under California law, such as breath and blood tests, and optional tests, like field sobriety exercises and PAS devices. Without these tests, there is often insufficient evidence for the prosecution to secure a DUI conviction. While it’s rare for a DUI defense attorney to successfully get chemical test results completely suppressed, inaccuracies or procedure errors can be challenged in court, which may result in drivers facing lesser charges.
When hiring a DUI lawyer in Vista, always ensure your representative has a detailed understanding of evidence law, as this can dramatically affect your defense. Attorney Peter Liss has 40 years of experience showing why DUI test results may not be as reliable as they seem.
Types of DUI Tests in California
There are three basic types of DUI tests used in California:
Field Sobriety Tests (FSTs)
These are optional, subjective tests administered by the arresting officer. They are generally used to provide more evidence against a suspect.
Preliminary Alcohol Screening (PAS) Breath Tests
Also called Preliminary Breath Tests (PBTs), these handheld Breathalyzers are a quick pre-screening device. They are optional for adult drivers, but not for minors under 21 or those on probation. These devices are rarely used as evidence in DUI cases because individuals who fail the screeners are typically given an evidentiary breath test.
Evidentiary Chemical DUI Tests
Mandatory breath or blood tests measure Blood Alcohol Content (BAC) and form the key evidence in DUI cases. In suspected drug DUI cases, officers typically rely on blood draws, though less-reliable urine samples can be used in some limited cases.
About Pre-Arrest DUI Tests
| What to Know | Field Sobriety Tests | PAS Devices |
|---|---|---|
| Required? | No | Only for Minors |
| Accuracy | Least Accurate | Fairly Accurate |
| When is it Performed? | Before arrest | Before arrest |
| Potential Problems | Highly Subjective
Can be affected by environmental or medical factors | Only requires one breath sample Can be affected by medical or environmental factors |
About Evidentiary DUI Tests
| What to Know | Breath Tests | Blood Tests |
|---|---|---|
| Required? | Yes | Yes |
| Accuracy | Reasonably Accurate | Most Accurate |
| When is it Performed? | After arrest | After arrest |
| Potential Problems | Cannot be retested Can be affected by medical or environmental factors | Improper collection, poor storage, or contamination may affect sample BAC at time of testing may be different than at time of driving |
Field Sobriety Tests
Field sobriety tests (FST) are a series of activities that are designed to help an officer evaluate whether a DUI suspect is intoxicated without relying on a chemical test. The National Highway Traffic Safety Administration (NHTSA) approved three tests for use as courtroom evidence, though some officers still ask suspects to perform other activities.
“Together, the reliability of the three accepted field sobriety tests is estimated to be 82-91% accurate in ideal conditions,” explains attorney Liss. “However, I have seen that the accuracy of these tests drops dramatically under real-world conditions.”
While the tests are optional, police officers rarely inform suspects of their right to abstain. Fortunately, an experienced DUI lawyer can challenge the legitimacy of this evidence as part of your DUI defense.
The three accepted field sobriety tests used to screen for DUIs in California are the walk and turn, one-leg stand, and horizontal gaze nystagmus. Here’s what to know about each of these tests, including their relative accuracy, purpose, and ways your attorney can challenge the results:
The Walk and Turn Test
| What to Know | Walk and Turn (WAT) |
|---|---|
| Accuracy Level | 68-79% |
| Instructions | Walk heel to toe in a straight line, then turn and walk back |
| Purpose | Evaluating balance and ability to follow directions |
| Problems | Uneven pavement, mental or physical disability, and poor footwear |
The One-Leg Stand Test
| What to Know | One-Leg Stand (OLS) |
|---|---|
| Accuracy Level | 65-79% |
| Instructions | Stand on one leg while counting out loud |
| Purpose | Measuring balance and concentration under pressure |
| Problems | Footwear, injuries, mental conditions, and uneven surfaces |
The Horizontal Gaze Nystagmus Test
| What to Know | Horizontal Gaze Nystagmus (HGN) |
|---|---|
| Accuracy Level | 77-89% |
| Instructions | Follow a pen or light with your eyes without moving your head |
| Purpose | Look for involuntary jerking of the eye at certain angles |
| Problems | Eye conditions, fatigue, and poor test administration |
Other FSTs, including the “nose-touch” and the ability to recite the alphabet backward and similar tests, have been proven by the NHTSA itself to be scientifically inaccurate. Nevertheless, many officers still ask suspects to do these tasks and then attempt to use the defendant’s results to prove their guilt. While it is possible to dispute the results of any field sobriety test, any test other than the three listed above is considered to lack scientific merit.
Breath Tests in California DUIs
Breath tests, often referred to as Breathalyzers, are the best-known and most frequently used type of evidence in a DUI case. Many people are unaware that there is an alternate choice at all. But despite their widespread use, these devices are not always accurate.
Many factors can skew the results (although most tips about “beating the Breathalyzer” are merely myths). Some factors that may fool the breath test into thinking your Blood Alcohol Content (BAC) is higher than it actually is include:
- Chemicals in the testing area
- Your breathing pattern
- Recently drinking diet sodas
- Your body temperature
- Recently using hand sanitizer
- Using tobacco or a vape
- Temperature fluctuations in the testing area
- Using an asthma inhaler
The San Diego Police and Sheriff’s Departments use both handheld PAS and portable evidentiary breath tests that are installed in their vehicles. While juveniles and drivers on probation must submit to a PAS, this test is optional for other drivers. All drivers must submit to an evidentiary breath or blood test when requested.
“If you have any questions about whether you are required to take a breath test, ask the officer,” says attorney Liss. “Police are legally required to warn suspects of the consequences of refusing to take an evidentiary chemical test.”
Blood Tests in California DUIs
“The majority of DUIs in Vista involve Breathalyzer tests,” notes Liss. “However, blood tests are more commonly used in San Diego County DUI cases involving injury or death, since the suspects are often taken to the hospital, where these tests are administered.” Blood draws are also the primary DUI test used in cases involving drugs, since breath samples cannot test for substances aside from alcohol, and urine tests are not very reliable.
Fewer things can go wrong with a DUI blood test than with a breath test, and they are more accurate, leaving lawyers with fewer ways to challenge the results. However, a blood draw has the advantage of a stored sample that can be retested later.
Additionally, several procedures must be strictly followed for a DUI blood test result to be legally admissible; otherwise, an attorney may file a motion to suppress the evidence. Contamination, improper storage, a broken chain of custody, and more can provide grounds for your lawyer to challenge the results.
Deciding On a Breathalyzer Vs. Blood Test
Officers often ask suspects to take a breath test without informing them that they also have the option to take a blood test. However, you have the right to choose either type under the state’s Implied Consent Law if you have been accused of drunk driving. Those charged with drug DUI are usually required to take a blood test, though urine tests may be permitted in some rare cases.
An attorney like Peter Liss can challenge the charges regardless of the test you choose. Here’s how to decide on the best strategy for your situation:
| Condition | Action to Take |
|---|---|
| If You’re Sober | Take the blood test because it can be retested if the results are positive. |
| If You’re Drunk | Take the Breathalyzer since the lower accuracy makes it easier to challenge when things go wrong. |
| If You Aren’t Sure | Take the Breathalyzer if you started drinking within the last 30 minutes. Otherwise, it’s a toss-up. |
Implied Consent & DUI Testing
Under California’s Implied Consent Law (VC 23612), you must submit to a chemical test if probable cause exists for your arrest.1 “In San Diego County, DUI chemical test refusal will result in police obtaining a search warrant to draw your blood, and you still will be charged with drunk driving,” warns Liss. Violating the Implied Consent Law will also cause you to lose your driver’s license for at least a year, and you will face mandatory jail time if you are convicted.
To learn more about when this law applies and what happens if you refuse testing, visit our dedicated Implied Consent in California page.
How Accurate Are DUI Tests?
The estimated accuracy of DUI tests varies because a test administered by a trained professional under ideal conditions will naturally be more accurate than one administered by an amateur in real-world situations. Challenging the reliability of your DUI test results is one of the most common defense strategies for California attorneys.
Accuracy of Field Sobriety Tests
As stated above, each FST has a different level of reliability, ranging from 65% to 89% in laboratory settings. Taken together, the overall accuracy rate for all three tests is reported to be between 81% and 92%.
However, “while these tests may seem scientific, they are primarily based on officers’ subjective opinions and are often administered improperly,” explains Liss. Real-life freeway shoulders and sidewalks are rarely perfectly paved and flat, and test-takers are not always healthy, young individuals without vision issues who happen to be wearing sturdy, comfortable footwear.
Overall, researchers have found that Field Sobriety Tests yield false positives about 30% of the time. In fact, when researchers took a deeper look at the accuracy of the Gaze Nystagmus (HGN) test, they found that it constituted “deliberate fraud” on the part of the United States Department of Transportation.
Unfortunately, the strong precedent for the admissibility of these tests allows prosecutors to continue admitting them as evidence.
Accuracy of DUI Breath Tests
Each type of Breathalyzer has its own margin of error. PAS devices typically have a greater margin of error than evidentiary breath tests, which is why they cannot be used as evidence in court.
“The San Diego Sheriff’s Department uses the Intoximeters® Inc. Intox EC/IR II for evidentiary breath tests,” explains Liss. “These devices have an acceptable margin of error of plus or minus .01, so a reading at .08 could be slightly lower or higher without an external issue affecting the machine.” This accuracy rate is relatively standard among Breathalyzer devices, which is why a defense lawyer will always work to fight the DUI test if your results are close to the 0.08% BAC limit set under California law.
Even if your Breathalyzer results are not right at 0.08%, your attorney can still challenge the accuracy of your results, especially if you were a victim of any violations under California Code of Regulations Title 17. This law states that :
- Breathalyzers must be correctly maintained and recalibrated every 10 days or after 150 tests, whichever comes first.
- Officers must watch suspects for belching or regurgitation for 15 minutes before testing to avoid mouth alcohol from artificially inflating the results.
- Law enforcement personnel operating a Breathalyzer must be trained to use that specific device.
- Suspects must provide two breath samples that capture deep lung air from hard, consistent breathing.
Beyond that, certain medical conditions like Keto diets, diabetes, fevers, asthma, or acid reflux can make readings falsely inflated.
Accuracy of Blood Tests
While blood draws are the most reliable DUI test, there are still some factors that may allow your attorney to challenge the results. Title 17 violations affecting blood tests include:
- Delaying the blood draw enough that it no longer shows the BAC at the time of driving, supporting a “rising alcohol defense.”
- Allowing an improperly trained or unauthorized individual to perform the blood draw.
- Contaminating the blood draw site by using an alcohol-based wipe to sterilize the skin.
- Using vials that lack sufficient anticoagulant or preservatives.
- Failing to properly mix the blood with the anticoagulant or preservatives.
- Neglecting to draw enough blood to allow for an independent retest of the sample.
- Storing the samples at improper temperatures.
- Breaking or failing to properly document the chain of custody.
In many cases, your observations following a blood draw can help your attorney challenge these test results. Write down everything you remember about your arrest and DUI test as soon as possible to help support your case.
Common Defenses Against DUI Test Results
Any procedural issues mentioned above may be used to challenge the test results and support your defense. If you were subject to a Title 17 violation, for example, your attorney can file a motion to suppress the evidence under 1538.5 (PC). “While I rarely see chemical DUI tests completely suppressed in San Diego County, these factors can help build a case to have the charges reduced and may enable defendants to secure a wet reckless plea,” says Peter Liss.
To help build your case, your lawyer may file a discovery motion to review maintenance and calibration logs relating to the breath test, training records for the officer or the individual who administered the test, or documents related to the chain of custody used to transport the blood test. In some cases, he may even hire an expert toxicologist to provide testimony stating you were not intoxicated.
To learn more about defense strategies your attorney may use, review our dedicated DUI defenses page.
How a Vista DUI Lawyer Can Help
From calibration errors to improper handling of blood samples, there are countless ways a defense attorney may challenge your DUI test results. Vista lawyer Peter Liss has 40 years of experience identifying weaknesses in the prosecution’s evidence, and he can help you too.
Call (760) 643-4050 to schedule a free initial consultation to discuss your DUI test results.
Frequently Asked Questions About DUI Tests
Can I Refuse a Breath Test in California?
While you can request a blood test rather than a breath test, you are legally required to submit to a chemical DUI test under the Implied Consent Law. Failure to do so will result in an automatic license suspension.
Are Field Sobriety Tests Required?
No. Regardless of your age, probation status, or any other factor, you are never legally required to take a field sobriety test, and attorneys typically urge clients not to submit to these tests.
What Happens if the Police Mishandled my Blood Sample?
When police mishandle blood samples, the evidence may be suppressed in some cases. Even when this does not happen, the incorrect police procedure can boost your case and help your attorney secure minimal charges and sentencing.
Can I Take a Urine Test for DUI?
Not usually. However, there are rare cases where people suspected of driving under the influence of drugs may be given this option because a blood draw is not a suitable option. For example, if a drug DUI suspect has hemophilia, they may be offered a urine test rather than a blood test. Urine tests are offered less frequently because they are less reliable when it comes to the time and amount of drugs used.
Legal References
- Vehicle Code 23612 (VC) (California Legislative Information) ↩︎
