By Deandra Grant, J.D., M.S. (Pharmaceutical Science), ACS-CHAL Forensic Lawyer-Scientist
When a Texas law enforcement officer hands you an Intoxilyzer 9000 printout showing a BAC above the legal limit, that number carries enormous weight. Prosecutors treat it as objective science. Juries tend to accept it at face value. But the instrument that produced it operates on a fundamental assumption that the only compound present in your breath sample that absorbs infrared light at the wavelengths it measures is ethyl alcohol.
That assumption is not always correct.
A range of medical conditions, physiological states, dietary choices, and occupational exposures can introduce compounds into your breath or mouth that the Intoxilyzer 9000 may misread as alcohol or can cause the instrument to overestimate your BAC even when alcohol is present. Understanding which conditions create this risk, and how they interact with the instrument’s detection methodology, is the foundation of a breath test defense built on actual science rather than generic objection.
One procedural point that applies across several of the conditions below: Texas breath testing protocols require the administering officer to observe the defendant continuously for 15 minutes immediately before the test. That observation period exists specifically to guard against mouth alcohol contamination. If the observation period was not properly observed and documented, the foundational validity of the test is in question regardless of any medical condition and that is always one of the first things we examine.
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GERD and Acid Reflux
Gastroesophageal reflux disease causes stomach contents) including any alcohol present in the stomach) to move back up into the esophagus and oral cavity. When a reflux event occurs, alcohol vapor from the stomach can be present in the mouth at the time of the breath test. The Intoxilyzer 9000 is designed to sample deep lung air, which reflects blood alcohol concentration. It has no reliable mechanism to distinguish between alveolar air and alcohol vapor that originated in the stomach rather than the lungs.
The result is mouth alcohol contamination which is a phenomenon where residual alcohol in the oral cavity produces a reading that is significantly higher than the actual BAC. A reflux event immediately before or during the test, even one the defendant may not consciously notice, can produce a dramatically elevated result.
The instrument’s slope detector is designed to identify some mouth alcohol artifacts, but it is not a complete safeguard. A slope detector that did not flag an abnormality does not mean mouth alcohol was absent. It means the artifact was not severe enough to trigger the algorithm. When GERD is part of a defendant’s medical history, the interaction between reflux events and the observation period documentation is a critical line of inquiry.
Diabetes and Ketosis
Diabetes (particularly poorly controlled or undiagnosed diabetes) can produce measurable amounts of acetone in the breath through a process called ketosis. When the body cannot properly metabolize glucose, it turns to fat as an energy source. The metabolic byproducts of fat metabolism include ketone bodies, one of which is acetone.
Acetone is exhaled through the lungs. The Intoxilyzer 9000 uses infrared spectroscopy to identify compounds by their absorption of light at specific wavelengths and acetone absorbs infrared light at wavelengths that partially overlap with ethyl alcohol. Depending on the concentration of acetone in the breath and the specific detection channels the instrument uses, acetone can register as alcohol and inflate the reported BAC.
Diabetic ketoacidosis is a serious condition that can develop rapidly in Type 1 diabetics and can produce acetone concentrations in the breath that are substantial enough to produce a meaningfully elevated false reading. A defendant who appeared confused, unsteady, or otherwise symptomatic at the roadside may have been experiencing a metabolic crisis rather than alcohol impairment. Those two clinical pictures can look similar to an officer conducting a roadside investigation.
Non-Diabetic Ketosis: High-Protein and Ketogenic Diets
You do not need to be diabetic to be in ketosis. The metabolic state that produces acetone in the breath is triggered any time the body shifts from glucose to fat metabolism including in otherwise healthy individuals following ketogenic or very low-carbohydrate diets.
The ketogenic diet has become widespread. A defendant who has been following a strict low-carbohydrate diet for weeks or months may have chronic low-level ketosis with measurable acetone in their breath at baseline that is entirely unrelated to any alcohol consumption. If that defendant consumed even a modest amount of alcohol, the combination of actual BAC and acetone-related interferent can produce a breath test result that significantly overstates the alcohol component.
This is not a hypothetical edge case. It is a well-documented phenomenon in the forensic toxicology literature, and it is relevant in any case where the defendant’s dietary habits are known or can be established through medical records or personal history.
Fever and Elevated Body Temperature
The Intoxilyzer 9000’s conversion of breath alcohol concentration to estimated BAC relies on an assumed breath temperature of approximately 34 degrees Celsius which is the normal temperature of deep lung air. The instrument’s internal breath temperature sensor is designed to account for deviations, but the relationship between breath temperature and reported BAC is direct: higher breath temperature means more alcohol vapor per unit of air, which the instrument reads as a higher BAC.
A fever of even one or two degrees above normal can measurably elevate a breath test result. Published research on the temperature coefficient of breath alcohol testing suggests that for each degree Celsius of elevation in breath temperature above the assumed standard, the reported BAC may be inflated by approximately 6 to 8 percent. A defendant with a fever of 38.5°C rather than the assumed 34°C could see a reported BAC that overstates actual alcohol concentration by a meaningful margin.
If a defendant was ill at the time of arrest (running a fever from infection, flu, or any other febrile condition) and that condition was not documented or considered, the breath test result deserves scrutiny on this basis alone.
Occupational Chemical Exposure
The Intoxilyzer 9000’s infrared detection methodology identifies compounds based on how they absorb light at specific wavelengths. Ethyl alcohol has a characteristic absorption pattern but it is not unique. A number of compounds present in industrial and occupational environments share absorption characteristics that can register on the instrument.
Compounds that have been documented as potential interferents include toluene, xylene, acetone, methyl ethyl ketone, isopropanol, and various hydrocarbons and solvents. Individuals who work in painting, auto body repair, construction, manufacturing, chemical processing, dry cleaning, or laboratory environments may have occupational exposure to one or more of these compounds at levels that can affect a breath test result.
The practical defense implication: a defendant who works in an environment with regular chemical exposure, and who was tested shortly after leaving work, may have residual compounds in their respiratory tract that the Intoxilyzer 9000 cannot reliably distinguish from ethyl alcohol. The instrument’s interferent detection system provides some protection, but it does not screen comprehensively for all potentially interfering compounds and a result that was not flagged by the interferent detector is not necessarily free of interferent influence.
Medications Containing Alcohol or Interfering Compounds
A range of common medications contain ethyl alcohol as a carrier or preservative. Liquid formulations of cough syrups, oral rinses, certain herbal preparations, and some prescription liquid medications use alcohol as a solvent. If a defendant used such a medication shortly before the breath test, residual alcohol in the oral cavity can contaminate the sample. This is a mouth alcohol issue that is identical in mechanism to the GERD scenario, but with a different source.
Beyond alcohol-containing medications, certain compounds present in pharmaceutical preparations can potentially interfere with IR-based breath testing. Asthma inhalers, in particular, have been a subject of scrutiny in DWI litigation. Some propellants and active compounds used in metered-dose inhalers have absorption characteristics that may interact with the Intoxilyzer’s detection channels. The clinical and forensic literature on specific inhaler formulations and their effect on breath test results is an area where expert analysis is often warranted.
A complete medication history is part of what we establish in any breath test case where the reported result is inconsistent with the defendant’s described alcohol consumption or clinical presentation.
Case Results
What These Conditions Mean for Your Defense
None of the conditions described above automatically invalidate a breath test result. What they do is raise documented, scientifically grounded questions about whether the reported number accurately reflects the defendant’s blood alcohol concentration at the time of the test.
Establishing these questions as part of a defense requires more than asserting a medical history. It requires understanding the instrument’s methodology well enough to explain precisely how the condition interacts with it and presenting that explanation through expert testimony that a jury can follow and credit.
As an ACS-CHAL Forensic Lawyer-Scientist with a Master’s Degree in Pharmaceutical Science, I approach breath test evidence with a level of analytical depth that most defense attorneys cannot bring to these cases. The chemistry underlying each of these conditions (ketone body formation, infrared absorption spectra, the partition ratio and its temperature dependence, the pharmacology of alcohol-containing medications) is not foreign territory. It is the foundation of how I evaluate every breath test case at Deandra Grant Law.
If you have been charged with DWI in Texas based on a breath test result, and you have any of the medical conditions, dietary practices, occupational exposures, or medication histories described in this piece, that information is relevant to your defense and needs to be examined.
Breath Test Defense at Deandra Grant Law
Managing Partner Deandra Grant brings more than 30 years of DWI defense experience, a Master’s Degree in Pharmaceutical Science, and an ACS-CHAL Forensic Lawyer-Scientist designation to every breath test case. That combination of legal and scientific training means your case is evaluated not just as a legal matter, but as a forensic one. Call (214) 225-7117 or visit texasdwisite.com to schedule a confidential consultation.
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