Breath Tests vs. Blood Tests in DUI Cases

DUI cases may involve breath testing, blood testing, or both. A breath test estimates the amount of alcohol in a person’s system by measuring alcohol in the breath. A blood test measures alcohol or drugs in a blood sample.

Each type of test has different issues. Breath tests may involve questions about machine calibration, officer procedure, mouth alcohol, medical conditions, timing, and whether the device was used properly. Blood tests may involve questions about the blood draw, storage, preservatives, lab testing, chain of custody, and whether the sample was handled correctly.

A DUI blood test lawyer or breath test attorney can review the specific testing method used in your case and look for problems that may affect the reliability of the result.

Why BAC Testing Matters in California DUI Cases

California DUI cases may involve more than one legal theory. Prosecutors may claim that a driver was impaired, or they may focus on a reported BAC level. For many adult drivers, the common BAC threshold is 0.08 percent. Different limits may apply to commercial drivers, drivers transporting passengers for hire, underage drivers, or drivers on DUI probation.

Because BAC evidence can affect the charge, DMV action, negotiations, and trial strategy, it should be reviewed carefully. A reported BAC number is important, but it is not the only issue. The defense may also examine whether the result was reliable, whether the testing process followed required procedures, and whether the reported number accurately reflects the person’s BAC at the time of driving.

Timing of Chemical Testing

Timing can be an important issue in DUI breath and blood test cases. A test usually happens after law enforcement stops the driver, investigates the situation, makes an arrest, and transports or processes the person for chemical testing.

That means the test may not occur at the exact time of driving. In some cases, a person’s BAC may have been lower while driving and higher by the time the test occurred. This can become important when the reported result is close to the legal limit.

A defense lawyer may review:

• The time of driving
• The time of the traffic stop or accident
• The time of arrest
• The time of the breath or blood test
• The number of drinks allegedly consumed
• The timing of alcohol consumption
• Whether the reported BAC accurately reflects the time of driving

These timing questions may support a challenge to the prosecution’s interpretation of the test result.

Rising BAC Arguments

A rising BAC argument focuses on whether the driver’s blood alcohol concentration was still increasing after the traffic stop. Alcohol does not always enter the bloodstream immediately. Depending on the timing of drinking, food, body chemistry, and other factors, a person’s BAC may continue to rise after they stop driving.

This issue can matter when the prosecution relies heavily on a breath or blood test taken well after the driving occurred. If the person’s BAC was lower at the time of driving than it was at the time of testing, that may affect the defense.

Rising BAC arguments are fact-specific. They often require careful review of the timeline, test result, officer observations, statements, and available evidence.

Breath Test Calibration and Maintenance Issues

Breath testing machines must be properly maintained and used according to required procedures. If the device was not calibrated, checked, maintained, or operated correctly, the defense may question the reliability of the reported result.

A DUI breath test attorney may review:

• Device maintenance records
• Calibration records
• Accuracy checks
• Officer training
• Testing procedures
• Observation period issues
• Error messages or irregularities
• Whether the result was consistent with other evidence

Breath test evidence can seem scientific and precise, but the process still depends on equipment, procedures, and human handling. Any weakness in those areas may become important to the defense.

Officer Procedure During DUI Testing

Officer procedure matters in DUI testing. Law enforcement must follow rules when requesting, administering, and documenting chemical tests. If an officer skipped required steps, gave unclear instructions, failed to observe the driver properly, or documented the process poorly, those issues may affect the case.

Procedure may matter in several areas, including:

• The initial traffic stop
• Field sobriety testing
• Roadside breath screening
• Arrest decisions
• Post-arrest chemical testing
• Advisements about testing
• Refusal allegations
• Documentation in police reports

A careful review of officer conduct can help determine whether the prosecution’s evidence is as strong as it appears.

Blood Draw, Storage, and Chain of Custody

Blood testing can raise different defense issues than breath testing. A blood test depends on proper collection, labeling, storage, transportation, lab analysis, and documentation.

A defense lawyer may examine:

• Who performed the blood draw
• Whether proper procedures were followed
• Whether the sample was correctly labeled
• Whether the sample contained proper preservatives
• How the sample was stored
• How the sample moved from collection to testing
• Whether the lab followed required procedures
• Whether the chain of custody is complete

If the blood sample was mishandled, contaminated, stored improperly, or documented poorly, the reported result may be challenged.

Medical Conditions or Other Explanations

Some DUI cases involve medical conditions, physical symptoms, or other explanations that may affect officer observations or testing. Fatigue, illness, anxiety, diabetes, acid reflux, dental work, certain diets, medications, or medical episodes may influence how a person appears during a DUI investigation.

These issues do not apply in every case. However, when they are present, they may help explain symptoms that an officer interpreted as signs of impairment.

A defense lawyer may review whether medical or physical factors affected:

• Speech
• Balance
• Coordination
• Appearance
• Breath testing
• Field sobriety tests
• Officer observations
• The interpretation of the chemical test result

A DUI investigation should consider the full context, not just one number or one officer’s conclusion.

Roadside PAS Testing vs. Post-Arrest Chemical Testing

A roadside preliminary alcohol screening test, often called a PAS test, is different from a post-arrest chemical test. A PAS test is usually a handheld breath test used during the investigation. Officers may use it to help decide whether to make an arrest.

A post-arrest chemical test is typically used as evidence after the arrest. This may involve a breath test at a station or facility, or a blood test collected for lab analysis.

The difference matters because each type of test may carry different legal and evidentiary issues. A roadside PAS result may raise questions about device reliability, officer procedure, and whether the result should be used to support probable cause. A post-arrest breath or blood test may raise questions about chemical testing rules, timing, calibration, lab handling, and whether the result accurately reflects the time of driving.

Can a DUI Breath or Blood Test Be Challenged?

Yes. A DUI breath or blood test may be challenged when the facts support it. The defense may question the traffic stop, arrest, testing process, machine reliability, blood sample handling, officer procedure, timing, or interpretation of the result.

A challenge does not automatically mean the case will be dismissed. However, testing issues may affect negotiations, motions, trial strategy, or the strength of the prosecution’s case.

A DUI defense attorney can review the evidence and determine whether the breath or blood test creates a strong prosecution argument or whether there are problems that should be challenged.

Speak With a Murrieta DUI Breath and Blood Test Lawyer

If your DUI case involves a breath test, blood test, roadside PAS test, or disputed BAC result, you should have the evidence reviewed carefully. The reported number may be important, but the testing process and timing may be just as important.

The Law Office of H. Charles Gorian offers a free, private, no-obligation consultation for people facing DUI charges and other criminal defense matters in Murrieta, Temecula, and throughout Riverside County. We can review the situation, explain the next steps, and help you understand your options.

Contact The Law Office of H. Charles Gorian today to speak with a Murrieta DUI defense lawyer.