A California DUI investigation may involve several different types of testing, including field sobriety tests, roadside breath tests, post-arrest breath tests, and blood tests.
These tests are not all governed by the same rules.
Standard field sobriety tests are generally voluntary. For most adult drivers, a pre-arrest Preliminary Alcohol Screening (PAS) breath test is also generally voluntary. After a lawful DUI arrest, however, California’s implied-consent law generally requires drivers to submit to a chemical breath or blood test, and refusing a required test can lead to separate driver’s-license and criminal consequences.
Just as importantly, a breath or blood result of 0.08% or higher does not automatically establish guilt. DUI test results may be challenged based on timing, testing procedures, Title 17 compliance, instrument accuracy, sample handling, rising blood alcohol concentration, and other reliability issues.
The Nieves Law Firm represents people facing DUI charges throughout the Bay Area and evaluates how the government’s evidence was obtained, tested, and documented.
California DUI Tests at a Glance
| Test | When It Is Usually Used | What It Evaluates | Can It Be Challenged? |
| Field sobriety tests | Usually before arrest | Coordination, balance, attention, and physical observations | Yes |
| PAS breath test | Usually during the roadside investigation | Breath alcohol concentration | Yes |
| Post-arrest breath test | After a lawful DUI arrest | Breath alcohol concentration | Yes |
| Blood test | Usually after arrest | Alcohol or drugs in the blood | Yes |
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Quick Answers About California DUI Testing
Can You Refuse Field Sobriety Tests in California?
Generally, yes. Standard field sobriety tests are voluntary for adult drivers in California.
Refusing to perform them does not necessarily prevent an officer from making a DUI arrest. An officer may rely on other evidence, including driving behavior, statements, appearance, speech, odor of alcohol, or other observations when determining whether there is probable cause for an arrest.
Can You Refuse a Roadside Breathalyzer in California?
For most adult drivers, a pre-arrest Preliminary Alcohol Screening, or PAS, test is generally voluntary.
Different rules can apply to drivers under 21 and drivers who are subject to DUI probation or other special testing requirements.
A post-arrest chemical breath or blood test is different and is governed by California’s DUI implied-consent requirements.
Does a 0.08% Breath or Blood Result Automatically Mean You Are Guilty of DUI?
No.
For a prosecution under California Vehicle Code § 23152(b), the prosecution must establish that the driver’s blood alcohol concentration was 0.08% or higher at the time of driving.
A qualifying chemical test obtained within three hours of driving may support a rebuttable presumption concerning the driver’s BAC at the time of driving, but the test result, testing procedure, and relationship between the testing time and driving time may still be challenged.
Can a California DUI Breath Test Be Challenged?
Yes.
Potential challenges can involve:
- Failure to comply with required testing procedures
- Problems during the 15-minute pre-test period
- Breath samples that do not satisfy regulatory standards
- Instrument maintenance or accuracy issues
- Operator error
- Mouth alcohol
- Medical or physiological factors
- Whether the test accurately reflects BAC at the time of driving
Our Oakland DUI defense page discusses additional issues that may affect breath-test evidence, including Title 17 compliance, calibration, and proper administration.
Can a DUI Blood Sample Be Independently Tested?
Generally, yes.
California regulations require the remaining portion of a forensic alcohol blood sample to be retained for a specified period so that a defendant may have an opportunity to obtain independent analysis when sufficient sample remains.
What Are the Two Main Types of California Alcohol DUI Charges?
California Vehicle Code § 23152 recognizes two major alcohol-related DUI theories.
Vehicle Code § 23152(a): Driving Under the Influence
Under subsection (a), prosecutors generally must prove that alcohol impaired the driver’s ability to operate a vehicle with the caution of a sober person using ordinary care under similar circumstances.
Evidence may include:
- Driving pattern
- Physical appearance
- Speech
- Statements
- Field sobriety test performance
- Breath or blood testing
- Officer observations
A driver can potentially be charged under this section even if the driver’s BAC was below 0.08%.
Vehicle Code § 23152(b): Driving With a BAC of 0.08% or Higher
Under subsection (b), the prosecution generally must prove that the person drove a vehicle while having a BAC of 0.08% or more.
Chemical breath or blood testing is especially important in these cases, but the number shown on the test does not necessarily end the inquiry.
The defense may examine when the person drove, when the sample was collected, whether the testing procedures were followed, and whether the result accurately reflects the person’s BAC at the time of driving.
People dealing with their first arrest can also review our guide to a first DUI offense in California for more information about the criminal and driver’s-license consequences that may follow.
California’s criminal jury instructions address the two DUI theories separately. CALCRIM No. 2110 addresses driving under the influence, while CALCRIM No. 2111 addresses driving with a BAC of 0.08% or more.
What Are the Three Standardized Field Sobriety Tests in California?
The National Highway Traffic Safety Administration recognizes three standardized field sobriety tests commonly used during DUI investigations.
1. Horizontal Gaze Nystagmus
During the Horizontal Gaze Nystagmus, or HGN, test, the officer observes the driver’s eyes while moving a stimulus from side to side.
The officer looks for certain eye movements that may be associated with alcohol impairment.
2. Walk-and-Turn Test
The driver is generally instructed to take heel-to-toe steps along a line, turn in a particular manner, and return while following a series of instructions.
3. One-Leg Stand Test
The driver is typically instructed to raise one foot, maintain balance, and count aloud until instructed to stop.
The walk-and-turn and one-leg stand tests are often described as divided-attention tests because they require a person to listen to instructions while simultaneously performing physical tasks.
Are Field Sobriety Tests Reliable?
Field sobriety tests produce observations rather than a direct measurement of blood alcohol concentration.
Their reliability can therefore depend heavily on how the tests were administered and under what conditions.
A DUI defense attorney may examine whether:
- The officer was properly trained
- Instructions were given correctly
- The test was demonstrated correctly
- The driver understood the instructions
- The testing surface was level
- Lighting was adequate
- Traffic or emergency lights created distractions
- Weather affected the test
- Footwear affected performance
- An injury or medical condition affected balance or coordination
For example, balancing on one leg on a dark or uneven roadside while vehicles pass nearby is different from performing the same exercise on level ground in a controlled environment.
Why Body Camera Footage Can Matter
Body-worn camera and dash-camera footage may be especially important when evaluating field sobriety testing.
Video can show the instructions the officer actually gave, the conditions at the scene, and how the driver actually performed.
In some cases, that footage may support the officer’s written observations. In others, it may raise questions about whether the report accurately describes what occurred.
How Do California DUI Breath Tests Work?
California DUI cases commonly involve two very different types of breath testing.
Preliminary Alcohol Screening Test
A Preliminary Alcohol Screening, or PAS, test is usually administered with a handheld breath-testing device during the roadside investigation.
For most adult drivers who are not subject to special testing requirements, the PAS test is generally voluntary.
California Vehicle Code § 23612 generally requires officers requesting a PAS test from an adult driver to advise the driver that:
- The PAS test is being requested to help determine whether the driver is under the influence
- The driver has the right to refuse the PAS test
- Taking the PAS test does not satisfy the separate chemical-testing requirement that can apply after a lawful DUI arrest
Special rules may apply to drivers who are under 21 or subject to DUI probation conditions.
The distinction between roadside testing and post-arrest chemical testing is explained in more detail in our guide to California Vehicle Code § 23612 and implied consent.
Post-Arrest Chemical Breath Test
After a lawful DUI arrest, California’s implied-consent law generally requires chemical testing for alcohol or drugs.
In alcohol cases, a driver is generally offered testing in accordance with the options and procedures established by Vehicle Code § 23612.
Refusing a required post-arrest chemical test can create consequences beyond the DUI charge itself.
What Does Title 17 Require for a California DUI Breath Test?
California’s Title 17 regulations establish standards for forensic breath alcohol testing.
Among other requirements, they generally provide for:
- A continuous 15-minute period before breath collection during which the subject must not ingest alcoholic beverages or other fluids, regurgitate, vomit, eat, or smoke.
- Analysis of two separate breath samples.
- Results from the two samples that do not differ by more than 0.02 grams of alcohol per 210 liters of breath.
- Periodic instrument accuracy testing.
- Accuracy checks at intervals not exceeding 10 days or after every 150 subjects tested, whichever occurs first.
- Training requirements for breath-test operators.
- Records relating to instrument accuracy and testing procedures.
The DUI testing issues discussed by our defense team include the 15-minute pre-test period, breath-device calibration records, maintenance records, and laboratory procedures when chemical testing is at issue.
Does a Title 17 Violation Automatically Exclude a Breath Test?
Not necessarily.
In People v. Williams (2002) 28 Cal.4th 408, the California Supreme Court explained that compliance with Title 17 is not the only possible method for establishing the reliability of chemical-test evidence.
That means a Title 17 violation does not automatically make a breath or blood result inadmissible.
However, a meaningful departure from required procedures may still be important when challenging the reliability, foundation, or weight of the prosecution’s evidence.
Issues involving breath-test calibration, the pre-test period, and improper administration may therefore become important when evaluating the strength of a DUI case.
What Is California’s Three-Hour BAC Presumption?
For a DUI charge under Vehicle Code § 23152(b), the relevant issue is the driver’s BAC at the time of driving.
The chemical test, however, may not occur until sometime later.
California law provides a rebuttable evidentiary presumption when qualifying chemical testing occurs within three hours after driving and shows a BAC of 0.08% or higher.
The presumption does not make the chemical-test result conclusive.
The defense may present evidence challenging whether the result accurately reflects the driver’s BAC at the actual time of driving.
California’s jury instructions explain that jurors may consider the statutory presumption when its requirements are satisfied while still evaluating the other evidence presented in the case.
Can Your BAC Rise After You Stop Driving?
Yes.
Alcohol may continue being absorbed into the bloodstream after a person finishes drinking.
As a result, a person’s BAC can potentially continue rising after they stop driving.
This is commonly called a rising BAC issue.
For example, if someone consumed alcohol shortly before driving and was tested significantly later, it may be necessary to determine whether their BAC was still increasing between the time they drove and the time they were tested.
Relevant factors may include:
- When the person began drinking
- When the person stopped drinking
- How much alcohol was consumed
- When and what the person ate
- When driving occurred
- When the traffic stop occurred
- When each chemical sample was taken
A forensic toxicologist may sometimes use this information in a process known as retrograde extrapolation to estimate a person’s likely BAC at an earlier point in time.
Those calculations depend heavily on the underlying facts and assumptions used.
Can You Refuse DUI Tests in California?
The answer depends on what test is being requested and when it is being requested.
California’s DUI testing and implied-consent rules distinguish between field sobriety tests, preliminary roadside breath tests, and chemical testing following a lawful DUI arrest.
Can You Refuse Field Sobriety Tests?
Generally, yes.
Standard field sobriety tests such as the walk-and-turn, one-leg stand, and HGN test are generally voluntary for adult California drivers.
Refusing them does not necessarily prevent an arrest because an officer may still rely on other evidence when evaluating probable cause.
Can You Refuse a PAS Breath Test?
For most adult drivers, a pre-arrest PAS test is generally voluntary.
Different rules apply in some circumstances, particularly to drivers under 21 and drivers subject to DUI probation testing requirements.
Can You Refuse a Breath or Blood Test After a DUI Arrest?
This situation is different.
California’s implied-consent law generally provides that a person who drives in California is deemed to have consented to chemical testing under the circumstances specified by Vehicle Code § 23612 after a lawful DUI arrest.
A driver who refuses a legally required post-arrest chemical test can face consequences separate from the underlying DUI charge.
Depending on the circumstances, those consequences may include:
- Driver’s-license suspension or revocation
- Use of the refusal as evidence
- Additional consequences following a DUI conviction
The exact consequences can depend on factors such as prior DUI-related history and the circumstances surrounding the requested test.
Our article on California implied-consent law and chemical-test refusals explains these requirements and potential refusal consequences in more detail.
Blood testing also raises additional constitutional and warrant issues in certain circumstances, particularly when law enforcement seeks to obtain a blood sample without the person’s consent.
For that reason, whether a particular DUI refusal was lawful or what consequences follow should be evaluated based on the specific facts of the arrest.
How Can a DUI Blood Test Be Challenged in California?
Blood testing may appear more precise than roadside testing, but several stages occur between the blood draw and the final reported result.
Each stage may be important when evaluating reliability.
Blood Collection
California Title 17 contains requirements governing forensic alcohol blood collection.
Among other things, blood from a living person generally must be:
- Collected by venipuncture as soon as feasible
- Collected without using alcohol or another volatile organic disinfectant to clean the collection site
- Collected with appropriate sterile and dry equipment
- Placed in an appropriate container
- Properly preserved
Preservation and Sample Handling
A defense investigation may examine:
- What collection tube was used
- Whether the tube was properly sealed
- Whether preservative and anticoagulant were present
- How the sample was labeled
- How it was stored
- Whether storage conditions complied with laboratory procedures
Chain of Custody
The prosecution may need to establish that the blood sample tested by the laboratory is the same sample taken from the defendant and that its integrity was preserved.
Records may therefore be examined to determine who possessed the sample and when.
Laboratory Analysis
The defense may also examine:
- Laboratory testing methodology
- Instrument calibration
- Quality-control procedures
- Reference standards
- Laboratory records
- Whether the laboratory followed its validated procedures
Chemical blood-test cases can therefore require review of far more than the final reported BAC. Our attorneys discuss blood-draw, chain-of-custody, and laboratory testing issues that may be relevant when evaluating DUI evidence.
Can the Defense Independently Test a DUI Blood Sample?
California regulations provide for retention of the remaining portion of forensic blood samples so defendants have an opportunity to obtain independent testing when sufficient sample remains.
Independent analysis can sometimes confirm the government’s result. In other circumstances, it may identify a discrepancy or provide additional information relevant to the defense.
The availability of the remaining sample and the timing of a request should therefore be evaluated as early as possible.
Is There a Margin of Error for California DUI Breath or Blood Tests?
There is no single universal “margin of error” that automatically gets deducted from every California DUI breath or blood result.
For example, a reported BAC of 0.09% does not automatically become 0.08% or 0.07% merely because testing instruments operate within defined accuracy parameters.
That does not mean the reported result is beyond challenge.
For a breath test, the defense may examine:
- Instrument accuracy checks
- Maintenance records
- Test records
- Sample consistency
- Testing procedure
- Operator training
- The 15-minute pre-test period
- Potential mouth alcohol
For a blood test, the defense may examine:
- Sample collection
- Preservation
- Chain of custody
- Laboratory calibration
- Quality controls
- Analytical methodology
- Independent retesting
These issues can become especially significant when the reported BAC is close to California’s 0.08% threshold.
The important question is whether the particular test result offered in the case is sufficiently reliable and whether it accurately reflects the driver’s BAC at the legally relevant time.
What Evidence Can a California DUI Lawyer Review?
A DUI investigation should not necessarily stop with the police report or the number shown on a breath or blood test.
Depending on the case, a defense attorney may review:
- Body-worn camera footage
- Dash-camera footage
- Dispatch records
- Field sobriety test instructions
- Breath-test records
- Instrument accuracy and maintenance records
- Blood collection records
- Chain-of-custody documentation
- Laboratory worksheets
- Quality-control records
- Toxicology reports
- Medical information relevant to testing
- The timeline between drinking, driving, arrest, and testing
The goal is not simply to argue that DUI testing is unreliable in general.
The question is whether the officer, instrument, testing procedure, sample, and laboratory involved in this particular case produced reliable evidence.
A California DUI defense attorney may use these records to evaluate whether the prosecution’s chemical-test evidence accurately reflects what happened.
Frequently Asked Questions About California DUI Tests
What Tests Do Police Use for a DUI in California?
Police may use field sobriety tests, a roadside PAS breath test, a post-arrest evidentiary breath test, or a blood test depending on the circumstances of the investigation.
Are Field Sobriety Tests Mandatory in California?
For most adult drivers, standard field sobriety exercises are generally voluntary. Different rules apply to chemical testing after a lawful DUI arrest.
Is a Roadside Breathalyzer Mandatory in California?
A pre-arrest PAS test is generally voluntary for most adult drivers. Special rules can apply to drivers under 21 and drivers on DUI probation.
What Happens If You Refuse a Breath or Blood Test After a DUI Arrest?
A refusal of a legally required post-arrest chemical test may result in driver’s-license consequences and may have additional consequences in a criminal DUI case.
California’s implied-consent law governs many of the requirements and consequences associated with post-arrest chemical testing.
The exact result depends on the circumstances and the driver’s prior history.
Can a 0.08% BAC Result Be Challenged?
Yes.
A 0.08% or higher result does not prevent a defendant from challenging the testing procedure, instrument reliability, timing of the test, rising BAC, sample handling, or other issues.
What Is Title 17 in a California DUI Case?
Title 17 of the California Code of Regulations contains rules governing forensic alcohol testing, including procedures and standards related to breath and blood testing.
These regulations can become important when evaluating whether chemical-test evidence was collected and analyzed reliably.
Can a DUI Blood Test Be Retested?
California regulations provide for retention of remaining forensic blood samples, and a defendant may be able to request a portion for independent testing when sufficient sample remains.
Does a Title 17 Violation Automatically Dismiss a DUI Case?
No.
A Title 17 violation does not automatically result in dismissal or automatically exclude a chemical-test result.
However, violations may be relevant when challenging the reliability, foundation, or weight of the evidence.
What Is the Difference Between a PAS Test and a Post-Arrest Breath Test?
A PAS test is generally a handheld roadside breath test used during the DUI investigation before arrest. For most adult drivers, it is generally voluntary.
A post-arrest chemical test is different. After a lawful DUI arrest, California’s implied-consent requirements generally apply.
For a more detailed explanation, see our guide to California implied-consent law under Vehicle Code § 23612.
Talk to a California DUI Defense Attorney
DUI testing can involve much more than a single breath or blood result.
The timing of the test, how the officer administered it, whether California testing regulations were followed, how a blood sample was handled, and whether the reported BAC accurately reflects the driver’s BAC at the time of driving can all matter.
The Nieves Law Firm represents people facing DUI and other criminal charges throughout California.
Learn more about how our DUI defense attorneys evaluate DUI evidence, or schedule a consultation to discuss your case.
This article provides general information about California DUI law and forensic alcohol testing. It is not legal advice and does not create an attorney-client relationship. Laws and procedures may change, and the application of the law depends on the facts of each case. Prior results, if discussed elsewhere on this website, do not guarantee or predict the outcome of any other case.
Reviewed by Jo-Anna Nieves, California Criminal Defense Attorney
Last reviewed: October 8, 2026
This article was reviewed for legal accuracy by Jo-Anna Nieves, founder of The Nieves Law Firm, a California criminal defense firm representing individuals charged with DUI and other criminal offenses.
Legal Sources & Authorities
This article discusses California DUI testing laws and procedures reflected in the following authorities:
- California Vehicle Code § 23152(a)-(b) — California DUI offenses and BAC-related provisions
- California Vehicle Code § 23612 — implied consent, PAS advisements, chemical testing, and refusal requirements
- 17 CCR § 1219 — preservation of the identity and integrity of forensic alcohol samples
- 17 CCR § 1219.1 — blood collection, handling, and retention requirements
- 17 CCR § 1221.1 — authorized breath-testing procedures and the 15-minute pre-test period
- 17 CCR § 1221.2 — duplicate breath samples, instrument accuracy standards, and operator training
- CALCRIM No. 2110 — Driving Under the Influence
- CALCRIM No. 2111 — Driving With 0.08 Percent Blood Alcohol
- People v. Williams (2002) 28 Cal.4th 408 — Title 17 compliance and the admissibility/reliability of chemical-test evidence
