Chemical Testing

Breath and Blood Testing in Arizona DUI Cases

Chemical tests — breath and blood — are the primary evidence used to prosecute DUI cases. While these tests are often presented as highly accurate, the science tells a more nuanced story. Understanding how these tests work and their limitations is essential to any DUI defense.

Breath Testing

Breath testing devices (such as the Intoxilyzer 8000) estimate blood alcohol concentration by measuring alcohol in a breath sample. The device uses infrared spectroscopy to detect ethanol molecules.

Known Issues with Breath Testing:

1. Mouth Alcohol Contamination — Residual alcohol in the mouth from burping, belching, GERD (acid reflux), or recent use of mouthwash or breath spray can dramatically inflate readings. Officers are required to observe a 15-20 minute deprivation period before testing.
2. Gastroesophageal Reflux (GERD/Heartburn) — Acid reflux can bring alcohol vapor from the stomach into the mouth, causing falsely elevated readings even during the observation period.
3. Ketones and Diabetes — Individuals with diabetes, those on low-carb diets, or those in a state of ketoacidosis can produce acetone and other ketones that breath testing devices may misidentify as ethanol.
4. Instrument Calibration — Breath testing devices must be regularly calibrated and maintained. Failure to follow calibration schedules or use proper solutions can lead to inaccurate results.
5. Temperature Variations — Breath testing assumes a body temperature of 98.6°F. Elevated body temperature (from fever, exercise, or being in a hot patrol car) can cause higher readings.
6. Radio Frequency Interference (RFI) — Electronic devices near the breath testing instrument can potentially interfere with readings.
7. Partition Ratio Assumptions — Breath testing relies on an assumed 2100:1 blood-to-breath ratio, but this ratio can vary significantly between individuals (from 1300:1 to 3100:1).

Blood Testing

Blood testing is generally considered more accurate than breath testing, but it is not without issues.

Blood Draw Issues:

• Improper draw site — The draw site must be cleaned with a non-alcohol-based antiseptic. Using an alcohol swab can contaminate the sample.
• Qualification of phlebotomist — The person drawing your blood must be properly trained and qualified.
• Proper equipment — Gray-top tubes with sodium fluoride (preservative) and potassium oxalate (anticoagulant) must be used.
• Chain of custody — The sample must be properly labeled, stored, and transported to the lab.

Lab Analysis Issues:

• Fermentation — If a blood sample is improperly preserved, bacteria and yeast can ferment glucose into alcohol, creating ethanol that was never in the driver’s blood.
• Coagulation — If blood clots in the tube (due to insufficient anticoagulant), the resulting plasma will have a higher alcohol concentration than whole blood.
• Lab contamination — Cross-contamination between samples, unclean equipment, or lab errors can affect results.
• Storage conditions — Improper storage temperature or prolonged storage can degrade the sample.
• Gas chromatography calibration — The testing instrument must be properly calibrated with known reference standards.

Why These Materials Matter: Chemical test results are not infallible. Blood samples can be contaminated, ferment, or be improperly stored. Breath machines have known error rates and environmental sensitivities. A thorough defense examines calibration records, collection procedures, chain of custody, and lab protocols against established standards.