How Medical Conditions Affect Breath Test Accuracy

Overview of Breath Testing in Calgary DUI Investigations

Breath testing is a key part of impaired driving investigations in Calgary, and understanding how it works is essential for building an effective legal defence. The Calgary Police Service (CPS) follows a strict, standardized process when conducting breath tests under the Criminal Code of Canada.

Roadside Approved Screening Devices (ASDs)

When a driver is stopped on suspicion of impaired driving, CPS officers typically begin by using an Approved Screening Device (ASD) at the roadside. These portable devices are designed to detect the presence of alcohol in a driver’s breath and determine whether further testing is necessary. If the ASD registers a “fail” result (usually corresponding to a Blood Alcohol Concentration (BAC) of 0.08 or higher), the officer will place the driver under arrest and transport them to a CPS detachment for further testing.

Intoxilyzer Testing at CPS Stations

Once at the station, drivers are tested on a calibrated Intoxilyzer, which is a more sophisticated and legally recognized device for determining BAC. Officers must follow strict protocols, including ensuring two separate breath samples are taken within a prescribed interval. These results are used as primary evidence in court.

Legal Requirement to Test Within Two Hours

Canadian law imposes a two-hour rule: breath samples must generally be taken within two hours of the time the driver was last operating the vehicle.  

Alberta’s Immediate Roadside Sanctions (IRS)

In Alberta, the Immediate Roadside Sanctions (IRS) Program allows CPS officers to impose administrative penalties based on breath test results — even before a criminal charge is laid. Penalties can include immediate licence suspensions, vehicle seizures, and mandatory education  

Medical Conditions That Can Affect Breath Test Results

Certain medical conditions can interfere with the accuracy of breath test results, leading to potentially misleading BAC readings. In Calgary DUI cases, understanding these factors can be critical for building a strong legal defence.

Gastroesophageal Reflux Disease (GERD) and Acid Reflux

Individuals with GERD or chronic acid reflux may experience mouth alcohol contamination during a breath test. Alcohol vapours from the stomach can rise into the mouth and throat, artificially inflating the BAC reading on an ASD or Intoxilyzer. Calgary defence lawyers often raise this issue when cross-examining officers or presenting medical evidence in court.

Diabetes and Ketoacidosis

People living with diabetes can develop a condition called ketoacidosis, which causes the body to produce acetone. Some breath testing devices can mistake acetone for ethanol, resulting in a false positive or exaggerated BAC reading. Defence lawyers in Calgary may request medical records and expert toxicology reports to challenge these results.

Respiratory Conditions (COPD, Asthma)

Conditions like chronic obstructive pulmonary disease (COPD) and asthma can make it difficult to provide a proper breath sample. This may lead to “insufficient sample” warnings or erratic readings. Lawyers may argue that these issues compromise the reliability of the test and should be taken into account by the court.

Recent Surgeries or Medical Devices

Certain medical interventions — such as tracheostomy tubes or recent throat surgeries — can affect how a person exhales during a breath test. If a Calgary driver has undergone surgery or uses medical devices that alter their airflow, their lawyer can present this evidence to question the validity of the test results.

Medications and Alcohol-Based Products

Many over-the-counter medications, cough syrups, and even alcohol-based mouthwash can leave short-term traces of alcohol in the mouth. These substances can produce false positive results if a breath test is taken soon after use. In Calgary, experienced DUI defence lawyers may subpoena pharmacy or medical records to show that a client’s positive test was not due to alcohol consumption.

How These Conditions Lead to False Positives

Medical conditions can create false positives or artificially high BAC readings, which is why courts in Calgary carefully scrutinize breath test evidence. Understanding the science behind these errors helps build stronger legal arguments.

Mouth Alcohol Interference

When alcohol vapours linger in the mouth or throat — whether from GERD, acid reflux, or recent use of alcohol-containing products — they can contaminate the breath sample. Breath testing devices like the Intoxilyzer 8000C, used by the Calgary Police Service, assume that the air being measured comes from deep in the lungs (alveolar air). If mouth alcohol is present, the device may register a much higher BAC than what is truly in the bloodstream.

Case Examples of Inaccurate Results

Canadian case law has recognized that medical issues can lead to unreliable breath test readings. For example, there have been cases where defendants with chronic acid reflux or poorly managed diabetes successfully challenged their results, leading to acquittals. These examples highlight the importance of presenting medical documentation and expert testimony in Calgary courts.

Artificially High Readings Without Significant Alcohol Intake

Conditions such as diabetic ketoacidosis produce acetone in the body, which can be misinterpreted by certain devices as ethanol. Similarly, individuals with respiratory conditions may have difficulty providing a consistent, deep lung sample, resulting in erratic readings that overestimate BAC. Even those who used mouthwash or cough syrup shortly before being stopped could appear over the legal limit, despite minimal or no alcohol consumption.

Role of Expert Witnesses in Calgary DUI Cases

Expert witnesses play a crucial role in challenging breath test results in Calgary impaired driving cases. Their testimony helps judges understand the scientific and medical factors that may have led to false positives or inflated BAC readings.

Toxicologists and Medical Experts

Toxicologists are often called upon to explain how breath testing devices work and why certain conditions — like GERD, diabetes, or COPD — can interfere with their accuracy. Medical specialists may testify about a defendant’s specific health condition, offering insight into how it could have contributed to an unreliable reading on the Intoxilyzer 8000C used by the Calgary Police Service.

Showing the Link Between Condition and BAC Results

An effective defence involves more than simply stating that a client has a medical condition. Expert witnesses must clearly demonstrate how that condition affected the blood-to-breath alcohol ratio or caused mouth alcohol contamination. This scientific connection is often critical for persuading the court that the reading does not reflect the driver’s true level of impairment.

Using Credible, Peer-Reviewed Evidence

Calgary defence lawyers strengthen their arguments by presenting peer-reviewed research studies and widely accepted scientific literature. This ensures that the evidence is not just anecdotal but grounded in sound science. Credible expert testimony can lead to evidence being excluded, charges being reduced, or even complete acquittals.

Steps to Take If You Have a Medical Condition and Are Charged

Inform Your Calgary Impaired Driving Lawyer

Be upfront with your lawyer about all health conditions, including GERD, diabetes, asthma, or any recent surgeries. The sooner your lawyer is aware of these details, the faster they can consult medical experts and begin building a strategy to challenge unreliable test results.

Gather and Preserve Medical Documentation

Collect medical records, prescriptions, and notes from your doctor that confirm your diagnosis and treatment history. These documents can be used in court to support the argument that your BAC reading was not an accurate reflection of your level of impairment.

Request Disclosure and Preserve Evidence

Your lawyer can make formal disclosure requests to the Crown for breathalyzer calibration logs, maintenance records, and officer notes. Acting quickly ensures critical evidence is preserved before it becomes unavailable, strengthening the case for having the test results excluded if they were affected by your condition.

Take Immediate Legal Action

Delaying legal advice can put your licence, job, and future at risk. Booking a consultation with a Calgary DUI defence lawyer allows you to explore possible medical defences, understand the legal process, and start protecting your driving privileges right away.