How Accurate Are Breathalyzer Tests in Texas?

The Intoxilyzer 9000: Austin’s Breath Testing Instrument

The Austin Police Department uses the Intoxilyzer 9000 for evidentiary breath testing in DWI cases. Texas DPS operates a regulated breath-testing program with standardized calibration procedures and certified operators. The instrument does not measure blood alcohol directly. It measures alcohol in a breath sample and reports a result based on a standardized breath-to-blood relationship. Scientific literature, including NHTSA materials, acknowledges that breath-to-blood relationships and testing conditions can vary among individuals. Whether that variation, or any other factor, materially affected a particular result depends on the individual test, the records, and expert review.

Factors That Can Be Evaluated in a Breath Test

None of the factors below automatically makes a breath-test result unreliable. Each is an issue the defense can evaluate to determine whether it materially affected the reliability of a particular test.

Breath-to-blood relationship. The instrument reports results using a standardized conversion. Individual physiology can vary from that standard. Whether individual variation is significant in a given case is a question for qualified expert analysis.

Mouth alcohol. Alcohol from belching, regurgitation, recent mouthwash use, or dental conditions can affect a breath sample. The required pre-test observation period and the instrument's own design are intended to address this. Whether the observation period was properly conducted and documented can be reviewed.

Radio frequency interference. The Intoxilyzer 9000 includes RFI detection. Whether the testing environment raises any interference issue can be evaluated from the records and circumstances.

Medical and dietary conditions. Conditions such as diabetes, ketosis, acid reflux, or GERD are sometimes raised in breath-test cases. Whether any such condition could have affected a particular result is a scientific question that depends on the individual and should be evaluated with qualified expert input.

Body temperature. Physiological conditions at the time of the test, including elevated body temperature, are sometimes raised as factors. Their effect in a given case requires expert evaluation.

The Maintenance and Calibration Record

Each Intoxilyzer 9000 has a maintenance history, including calibration logs, reference solution changes, accuracy checks, and error logs, which can be requested. The firm requests the maintenance records for the specific instrument used in the test. Findings that can be relevant to a BAC challenge include:

• Missed or irregular calibration checks
• Reference solution issues
• Logged instrument errors near the date of the test
• Lapsed operator certification for the testing officer

Whether any record issue affects the admissibility or weight of a result depends on its legal and scientific significance.

Blood Tests Can Also Be Evaluated

Blood evidence can be reviewed for the warrant, collection procedure, preservation, storage, chain of custody, and laboratory analysis. Whether any issue, including a preservation or storage question, affected the result is a scientific question that depends on the facts and expert review.

What This Means for Your Austin DWI Case

A BAC result above 0.08 is evidence, not a verdict. An Austin DWI attorney can request the maintenance records and operator certification and evaluate the testing circumstances to determine whether any factor materially affected the reliability of the result. The question is whether the result reliably reflects alcohol concentration as required by Texas law.