What Can Cause a False Positive on a Maryland Breath Test?

 Posted on May 27, 2026 in DUI

If you blew into a breathalyzer and got a result that does not reflect how much you actually had to drink, you are not alone. Breath tests are treated as powerful evidence in DUI cases, but they are not perfect. Several medical conditions, medications, foods, and equipment problems can produce a result that shows alcohol when little or none is actually present. If you are facing a DUI charge in 2026 based on a breath test result you believe was wrong, our Montgomery County DUI defense lawyers can review your case and help you understand whether the result can be challenged.

Under Maryland Transportation Code Section 16-205.2, the preliminary breath test officers use on the roadside is not admissible as evidence in court. It is only used to help the officer decide whether to make an arrest. The evidentiary breath test given at the police station is a different matter. Under Maryland Courts and Judicial Proceedings Section 10-309, those results are admissible in court and can be used against you. But admissible does not mean unbeatable. That result can still be challenged.

Can Medical Conditions Cause a False Positive on a DUI Breath Test?

Several medical issues can directly affect what a breathalyzer reads, even when you have had little or no alcohol.

GERD and Acid Reflux

Gastroesophageal reflux disease, commonly called GERD, is one of the most well-known causes of false or inflated breath test results. GERD causes stomach contents, including stomach acid and any alcohol in the stomach, to come back up into the throat and mouth. A breathalyzer is designed to measure alcohol in deep lung air. When stomach alcohol is present in the mouth or throat, the machine can pick it up and produce a reading that is significantly higher than your actual blood alcohol level.

If you have a documented history of GERD or acid reflux, that medical history can be an important part of your defense. It is one of the reasons your attorney will ask about your health before building your case strategy.

Diabetes and Low-Carb Diets

People with diabetes or those following a very low-carbohydrate diet can produce a substance called acetone in their breath. Certain compounds, including acetone, may interfere with some breath-testing devices or contribute to inaccurate readings under certain conditions. This means a person with diabetes who has consumed no alcohol at all can show a positive reading on a breathalyzer simply because of how their body is processing energy.

Fever and Elevated Body Temperature

Body temperature affects how breath test machines calculate BAC. These devices are calibrated based on an assumed breath temperature. When your actual body temperature is higher than normal, such as when you have a fever or are ill, the machine can overestimate your BAC. Research has shown that elevated body temperature can affect the accuracy of some breath test results.

Can Medications and Products Cause a False Positive on a Breathalyzer Test?

Several common medications and everyday products contain alcohol or compounds that can interfere with a breathalyzer reading.

Over-the-counter cough syrups, cold medicines, and throat sprays often contain alcohol as an ingredient. If you used one of these products shortly before being pulled over, residual alcohol in your mouth can skew the test result significantly. Mouthwash is another common culprit. Many mouthwashes contain alcohol. If you used one recently, it can produce a reading that has nothing to do with drinking.

Certain asthma inhalers and other medications can also introduce compounds into your breath that interfere with the machine's accuracy. Some prescription medications for diabetes, heart conditions, and other chronic illnesses can affect how the body produces or breaks down certain compounds that breathalyzers may read as alcohol.

Can Equipment Problems Cause a False Positive on a Breath Test During a DUI Stop?

A breathalyzer is a machine, and like any machine, it requires proper maintenance and regular calibration to work correctly. If it is not serviced on schedule or is not operating within its required tolerances, the results it produces are not reliable.

In Maryland, breath test machines used as evidence must be properly maintained and operated according to established protocols. Your attorney can request the maintenance and calibration records for the specific machine used in your case. If those records show the machine was overdue for service, had been repaired recently, or had produced inconsistent results, that creates a real basis to challenge your reading.

Operator error is another factor. The officer administering the test must follow specific procedures for the results to be valid. For example, officers are required to observe you for a set period before administering the test to make sure you have not belched, vomited, or put anything in your mouth that could affect the reading. If that observation period was not properly followed, the result may be challengeable.

Does the Timing of a Breathalyzer Test Matter?

Alcohol is absorbed into the bloodstream at a rate that varies from person to person. In some cases, if you were pulled over shortly after having a drink, your BAC may still have been rising at the time of the test. That means the reading taken at the roadside or the police station might actually be higher than your BAC was at the time you were driving, which is what the law is actually concerned with. This is sometimes called the rising BAC defense, and it is a legitimate argument in cases where the timing between driving and testing was significant.

Schedule a Free Consultation With Our Silver Spring, MD DUI Defense Lawyers

A breath test result that does not reflect what actually happened is not something you should simply accept. At The Law Offices of Gerstenfield & Demirji, PC., we bring warmth and compassion to every case while still being aggressive when the situation calls for it. You deserve a defense that takes every angle seriously. Call 301-589-9500 today to schedule a free consultation with our Montgomery County, MD DUI defense attorneys. We are available 24/7.

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