Is It Better to Take a Breath Test or Blood Test After a DUI Arrest?

A DUI arrest in San Diego usually moves quickly. One minute you are on the side of the road, and the next you are being asked to choose between a breath test and a blood test. Many people assume the “better” choice is the one that gives the police less evidence. In California, the question is more complicated. After a lawful DUI arrest, refusing required chemical testing can create its own DMV and court problems, so the practical issue is often not whether to test, but which test creates the most defensible record under the circumstances.

The Law Office of Joshua R. Bourne represents people accused of DUI and other criminal offenses in San Diego. Attorney Joshua R. Bourne has more than 20 years of criminal defense experience and has represented clients in complex DUI cases since founding his firm in 2006. For someone facing a chemical test issue, the details matter: what the officer said, when the test was requested, whether drugs were suspected, whether the machine was working properly, and whether the result can be challenged.

The Short Answer: There Is No One Best Test for Every DUI Arrest

For many alcohol-only DUI arrests, a breath test may seem simpler because it is fast, noninvasive, and does not leave the government with a physical blood sample. A blood test may seem more precise, and it can sometimes give the defense an opportunity to retest the sample or challenge how it was collected, stored, transported, or analyzed. Neither option is automatically “better” in every case.

A breath test can be attacked when there are questions about calibration, maintenance, operator training, observation periods, mouth alcohol, breathing pattern, timing, or whether the reported number reliably reflects blood alcohol concentration at the time of driving. A blood test can be attacked when there are questions about chain of custody, contamination, preservatives, anticoagulants, lab procedures, delayed collection, or whether the sample was properly documented.

The best choice can also change if the officer suspects drug impairment. Breath testing is mainly useful for alcohol. If the officer believes drugs are involved, California law may allow the officer to require a blood test even after a driver has completed a breath test.

Chemical Testing After a California DUI Arrest

California’s implied consent law is found in Vehicle Code section 23612. In general, a person who drives in California is deemed to have consented to chemical testing of breath or blood for alcohol if lawfully arrested for DUI. For suspected drug impairment, the law focuses on blood testing because a breath device does not measure most drugs.

This post-arrest chemical test is different from a preliminary alcohol screening test, often called a PAS test, that may be requested before arrest. Most adult drivers who are not on DUI probation are not required to take a pre-arrest PAS test. A post-arrest chemical test is different. Once a lawful DUI arrest has occurred, refusal can trigger serious consequences.

For an alcohol DUI arrest, Vehicle Code section 23612 generally requires the officer to advise the person that they have a choice between breath and blood testing. If the chosen test cannot be completed, the driver may be required to submit to the remaining test. If neither breath nor blood is available in limited circumstances, urine testing can become an option.

Breath Testing After a DUI Arrest

A breath test estimates blood alcohol concentration by measuring alcohol in deep lung air. It is usually performed at a police station, jail, DUI processing facility, or other approved location using a breath testing instrument.

Possible Advantages of a Breath Test

A breath test is typically quick. The result is often available immediately, and the procedure does not involve needles. A breath test also does not create a vial of blood that can later be tested for substances beyond alcohol, although the facts of the case may still lead officers to seek additional testing if they suspect drugs.

Breath testing can also create defense issues. Breath machines do not directly measure alcohol in the blood. They estimate it. That means the defense may examine whether the device was properly maintained, whether the operator followed required procedures, whether the driver was observed long enough before the test, and whether burping, regurgitation, dental appliances, mouthwash, reflux, or other facts could have affected the reading.

Possible Disadvantages of a Breath Test

The main disadvantage is that a breath test produces a number immediately, and that number often becomes central to the prosecutor’s case. If the reported BAC is 0.08 percent or higher, the prosecutor may charge both driving under the influence under Vehicle Code section 23152(a) and driving with a blood alcohol concentration of 0.08 percent or more under Vehicle Code section 23152(b).

Breath testing can also be less useful for independent defense testing because there is no physical sample to retest later. The defense can review records, procedures, machine logs, maintenance documents, and officer conduct, but there is no saved breath sample to send to a separate laboratory.

Blood Testing After a DUI Arrest

A blood test measures alcohol or drugs in a blood sample. In a DUI case, the sample is typically drawn by a trained person and sent to a laboratory for analysis.

Possible Advantages of a Blood Test

A blood test is often viewed as more direct evidence of what was in a person’s system. That can sound bad for the defense, but it can also create opportunities. Because there is a physical sample, the defense may be able to investigate whether the sample was properly drawn, labeled, sealed, stored, transported, and tested. In some cases, a portion of the sample may be available for independent retesting.

Blood results can also raise timing questions. Alcohol levels rise, peak, and fall. A blood draw taken well after driving does not automatically prove what the person’s BAC was at the exact time of driving. Depending on the drinking pattern, food intake, and time of draw, the defense may explore whether the person’s BAC was still rising when they were pulled over.

Possible Disadvantages of a Blood Test

A blood test is invasive and leaves the government with a biological sample. If the case involves suspected drugs, a blood sample may be tested for controlled substances, prescription medications, cannabis, or other substances depending on the lab request and case facts. In a mixed alcohol and drug case, blood evidence can expand the scope of the prosecution’s theory.

What Happens if Drugs Are Suspected?

Drug DUI cases are different from alcohol-only cases. Vehicle Code section 23612 allows an officer to request an additional blood test after a breath test if the officer has reasonable cause to believe the driver was under the influence of drugs or a combination of alcohol and drugs and believes a blood test will reveal evidence of that impairment.

This is important because a driver may think, “I already took the breath test, so I am done.” In some cases, that is not true. If the officer lawfully requests an additional blood test under the drug impairment provisions, refusing or failing to complete the additional test can still create DMV consequences.

Drug DUI cases also do not work the same way as 0.08 alcohol cases. For many drugs, there is no simple per se number that proves impairment for every driver. The prosecution usually must connect the substance, timing, driving pattern, officer observations, field sobriety tests, and toxicology evidence to prove impairment.

Refusing a Breath or Blood Test Can Create Bigger Problems

Some people think refusal is the safest choice because it may keep the government from getting a BAC number. In California, refusal can make the case harder in other ways.

Under Vehicle Code section 23612, the officer must advise a driver of the consequences of failing to submit to or complete required testing. Administrative consequences can include a one-year driver’s license suspension for a first refusal, a two-year revocation if there is a qualifying prior within 10 years or prior administrative action, and a three-year revocation if there are two or more qualifying priors or prior administrative actions.

A refusal can also be used against the driver in court. For breath or urine refusals, Vehicle Code section 23578 allows the court to consider the refusal as a special factor that may justify enhanced sentencing if the person is convicted of DUI under Vehicle Code section 23152 or DUI causing injury under Vehicle Code section 23153. Vehicle Code section 23577 addresses mandatory punishment enhancements for willful refusal or failure to complete testing, but current law states that those penalties do not apply to a person who refused to submit to or complete a blood test under Vehicle Code section 23612. That does not erase DMV consequences for refusing a blood test, and it does not mean the refusal is harmless.

The DMV Case Is Separate From the Criminal Case

A DUI arrest usually creates two tracks. The criminal case is handled in court. The driver’s license case is handled through the DMV administrative process. The Law Office of Joshua R. Bourne notes that DMV hearing issues may include who was driving, whether the officer had probable cause, and whether there was evidence of a BAC of 0.08 or higher.

After a DUI arrest, the officer may take the California license and issue a temporary license. Missing the DMV deadline can limit options even if the criminal case is later reduced or dismissed.

A breath or blood result may be challenged in court, but it may also be central to the DMV hearing. A refusal allegation can affect the license case, the bargaining posture, and the sentence exposure if there is a conviction.

Which Test Is Easier to Challenge?

It depends on the facts. Breath tests often involve machine reliability, maintenance records, operator compliance, observation periods, mouth alcohol, and whether the breath result accurately reflects BAC at the time of driving. Blood tests often involve collection procedure, chain of custody, lab analysis, preservatives, storage conditions, contamination, and delayed testing.

A blood result may be easier to investigate scientifically because there may be a retained sample and a paper trail from draw to lab. But either test can be damaging if the procedure was clean and the number is high.

The more important question is usually not, “Which test is always better?” It is, “What can be challenged in this particular case?”

How a San Diego DUI Defense Lawyer Reviews Chemical Test Evidence

Attorney Joshua R. Bourne can examine the legality of the stop, the basis for the arrest, the advisement given before testing, the timing of the test, the officer’s reports, the breath machine records, lab documentation, body-worn camera footage, dispatch records, and DMV paperwork.

In a breath case, the defense may request calibration and maintenance records, operator training materials, testing logs, and documents showing whether the machine was approved and functioning correctly. In a blood case, the defense may review the blood draw procedure, chain of custody, lab protocols, analyst notes, storage records, and whether independent testing is available.

This review can affect negotiations, DMV strategy, motions, trial defenses, and sentencing arguments.

Speak With The Law Office of Joshua R. Bourne After a San Diego DUI Arrest

If you were arrested for DUI in San Diego and had to choose between a breath test and a blood test, the result is not the end of the case. Breath tests, blood tests, and refusal allegations can all be challenged when the facts support it. The most important step is to have the arrest, DMV paperwork, chemical test records, and police reports reviewed quickly.

The Law Office of Joshua R. Bourne represents clients facing DUI charges and license consequences in San Diego. Contact the firm to discuss what happened during your arrest, whether the chemical test was properly requested and administered, and what defenses may be available in your court and DMV proceedings.