Many people arrested for DUI assume their case is over as soon as a breath test shows a blood alcohol concentration of .08% or higher. That reading is important evidence, but it is not a verdict. Breath-testing results may be challenged when officers do not follow required procedures, the equipment is not properly maintained, or biological factors affect the sample.
Anyone facing a California DUI charge should understand how breath tests work and what can make a result less reliable. From Encino and the San Fernando Valley to courts throughout Southern California, an attorney may examine the testing process, maintenance records, medical history, and timing of the sample before determining how much weight the reported number should carry.
California law prohibits driving with a blood alcohol concentration, commonly called BAC, of .08% or higher for most adult motorists. BAC measures the amount of alcohol in a person’s blood. However, the prosecution must still connect the chemical-test result to the person’s alcohol level when they were driving.
How Accurate Are Breathalyzers in California?
Breath-testing devices do not directly measure the amount of alcohol in a person’s blood. They analyze alcohol in a breath sample and use that measurement to estimate BAC. The result can be useful, but its reliability depends on the condition of the device, the way the sample was collected, and whether the operator followed required procedures.
There is also an important difference between a roadside preliminary alcohol screening device and an evidentiary breath-testing instrument used after an arrest. A roadside device may help an officer investigate suspected impairment. A later evidentiary test is generally used as formal chemical-test evidence. The type of instrument, its records, and the circumstances of each test may all matter.
A DUI lawyer reviewing a breath-test case may ask several questions:
- Was the device approved and working properly?
- Were required accuracy checks and maintenance performed?
- Did the officer observe the driver before collecting the sample?
- Was the officer trained to operate that instrument?
- Could mouth alcohol or a medical condition have affected the reading?
- How much time passed between driving and testing?
No single issue automatically invalidates a result. The defense must evaluate how any error or irregularity affects the reliability and weight of the evidence.
How Title 17 Rules Affect Southern California Breath Tests
Title 17 of the California Code of Regulations establishes procedures for forensic alcohol testing. These regulations address matters such as sample collection, breath-testing instruments, accuracy checks, recordkeeping, and the qualifications of people who perform or oversee testing.
One frequently examined requirement is the observation period before a breath sample is collected. The person administering the test is expected to continuously observe the subject for at least 15 minutes. During that period, the subject should not eat, drink, smoke, vomit, regurgitate, or place anything in the mouth. These precautions are intended to reduce the risk that alcohol remaining in the mouth will distort the result.
An officer does not necessarily need to stare directly at the person every second. However, the evidence should support that meaningful, continuous observation occurred. A lawyer may review body-camera footage, station video, reports, dispatch records, and testimony to determine whether the officer was distracted, left the room, completed paperwork, or otherwise failed to monitor the person adequately.
Instrument records are another important part of a breath-test investigation. Title 17 requires periodic accuracy testing of breath-testing instruments. Depending on the applicable procedure, accuracy checks generally must occur at specified time or testing intervals. Maintenance records may show failed accuracy checks, error messages, repairs, irregular results, or gaps in documentation.
The defense may also examine whether the person operating the device met applicable training requirements. Poor technique, incomplete samples, failure to follow the instrument’s instructions, or an operator’s lack of familiarity with the equipment may become relevant when evaluating the result.
A violation of a testing regulation does not always cause a court to exclude the evidence automatically. It can, however, provide grounds to question the test’s foundation, accuracy, or persuasive value when considered with the rest of the case.
Can GERD or Mouth Alcohol Affect a Breath Test?
Breath-testing instruments are intended to analyze air from deep in the lungs. Alcohol remaining in the mouth can create a higher reading because the device may detect concentrated alcohol vapor that does not accurately represent alcohol circulating in the bloodstream.
Recent drinking, mouthwash, breath spray, some medications, vomiting, burping, or regurgitation may contribute to residual mouth alcohol. This is one reason the pretest observation period matters.
Gastroesophageal reflux disease, or GERD, is a condition in which stomach contents flow back into the esophagus. In an appropriate case, reflux occurring close to the test may raise questions about whether alcohol vapor entered the mouth and affected the sample. A diagnosis alone does not prove that a reading was inaccurate. The timing of symptoms, drinking history, observation-period evidence, medical records, and characteristics of the breath-test results all need to be considered.
Some modern instruments contain safeguards intended to identify mouth-alcohol patterns. Those safeguards are not a substitute for proper observation, and their effectiveness may depend on the instrument and circumstances.
Can a Keto Diet Cause a False Breathalyzer Reading?
A strict low-carbohydrate or ketogenic diet causes the body to produce ketones while burning fat for energy. One ketone-related compound, acetone, can be present in a person’s breath.
Claims that a keto diet automatically creates a false DUI result should be treated cautiously. Whether ketosis could interfere with a particular test depends on the instrument’s technology, its ability to distinguish alcohol from other compounds, and the evidence from that specific case. Newer evidentiary devices may use safeguards designed to reduce interference.
Still, diet, fasting, diabetes, medications, and other metabolic factors may be worth discussing with the defense lawyer and, when appropriate, a forensic toxicologist. A forensic toxicologist is a scientist who studies how alcohol and other substances are absorbed, distributed, and measured in the body.
What Is the Rising Blood Alcohol Defense?
California’s .08% DUI law focuses on BAC at the time a person was driving. A chemical test taken within three hours that shows a BAC of .08% or higher can create a rebuttable presumption that the driver was also at or above that level while driving. “Rebuttable” means the defense may present evidence challenging that conclusion.
Alcohol is not absorbed into the bloodstream immediately. After a person’s last drink, BAC may continue rising during what is called the absorption phase. The timing varies based on factors that may include the amount consumed, drinking pattern, food intake, body composition, and individual physiology.
Consider a driver stopped near Encino shortly after leaving a restaurant. The officer conducts an investigation, makes an arrest, transports the driver, and administers a later breath test. If the person had consumed alcohol shortly before driving, the BAC recorded at the station could be higher than the BAC when the vehicle was being operated.
This argument does not necessarily claim that the device malfunctioned. Instead, it challenges whether a later result accurately proves the driver’s BAC at the legally relevant time.
A toxicologist may perform a retrograde analysis, meaning a scientific estimate of an earlier BAC based on the known timeline and available evidence. Receipts, surveillance footage, witness accounts, phone records, roadside results, and the timing of each drink may become important. Because alcohol absorption and elimination differ among individuals, any estimate should be based on the actual facts rather than a generic formula.
How a DUI Attorney Can Challenge Breath-Test Evidence
Strong breath-test challenges often involve several related issues rather than one dramatic flaw. For example, the evidence may show an incomplete observation period, inconsistent breath samples, a delayed test, relevant reflux symptoms, or maintenance records that call the instrument’s performance into question.
A criminal defense attorney may seek:
- Breath-device maintenance and accuracy-check records
- Officer training and certification documents
- Body-camera, station, and booking-area video
- Electronic data generated by the testing instrument
- Roadside and evidentiary test results
- Medical records relevant to GERD or other conditions
- Analysis from a qualified forensic toxicologist
Not every irregularity will result in dismissal or suppression of the test. However, identifying weaknesses may affect pretrial motions, negotiations, DMV proceedings, or how a judge or jury evaluates the prosecution’s evidence.
Speak With a Southern California DUI Lawyer
A breath-test reading above .08% does not remove your right to examine the evidence or challenge the prosecution’s conclusions. The instrument, operator, testing conditions, biological factors, and delay between driving and testing may all deserve careful review.
Karpel Law Group represents people facing DUI allegations in Encino, the San Fernando Valley, Los Angeles, and throughout Southern California. Our law firm can evaluate the breath-test evidence, explain the criminal and DMV processes, and identify defenses supported by the facts. To discuss your arrest with a DUI lawyer, contact our criminal defense team.