Breathalyzer Tests Can Be Inaccurate

There are numerous reasons why a breathalyzer test can result in an inaccurate reading, which may result in a serious crime such as a DUI. Consult your Virginia Beach Criminal Lawyer for a specific analysis of your case.

In Virginia, a BAC of .08% or more is sufficient to convict. The defense, however, may present “rebuttal” evidence that the results of the breathalyzer test were inaccurate. As a result, evidence regarding the time frame the accused drank the alcohol, as well as the amount consumed, are both relevant inquiries. Expert testimony regarding the margin of error in breathalyzer tests is admissible, but does not by itself rebut the presumption.*

Less Breathing Prior to Blowing May Lead to Higher (and Inaccurate) BAC Levels

The best step to take after charges arise from DUI/DWI is to consult your local Virginia Beach Criminal Lawyer. A recent medical study has shown that the pattern of a person’s breathing can drastically affect the blood alcohol content (BAC) reading. Somewhat alarmingly, the study reported that where a person held his or her breath for 30 seconds prior to blowing into a breathalyzer device, the BAC level increased by 15.7%.** This margin could be the difference between an arrest and your freedom. Consult your Virginia Beach criminal lawyer if you believe you have been the victim of an inaccurate breathalyzer reading. The study above also found that by breathing faster (i.e., hyperventilation), BAC readings were lower. For example, the study found that by running up a flight of stairs prior to breathing into a breathalyzer device, results were 11 to 14% lower.

Instructions from Police Officers May Lead to Higher BAC Levels

Police offices are sometimes trained to instruct DUI suspects to “blow hard and deep” into the breathalyzer device, ensuring that the deep portions of the lungs have excreted all the air. Such instructions can lead to inaccurate results, due to the reasoning explained below by Professor Hlastala.***

According to Professor of Physiology, Biophysics and Medicine at the University of Washington, Dr. Michael Hlastala:

“[T]he most overlooked error in breath testing for alcohol is the pattern of breathing . . . . the last part of the breath has an alcohol concentration that is much higher than the equivalent BAC. The last part of the breath can be over 50% above the alcohol level . . . . Thus, a breath tester reading of .14% taken from only the last part of the breath may indicate that the blood level is only .09%.” ****


* Lemond v. Com., 19 Va. App. 687, 454 S.E.2d 31 (1995); Nelson v. Com., 16 Va. App. 266, 430 S.E.2d 553 (1993).

** “How Breathing Techniques Can Influence the Results of Breath-Alcohol Analyses,” 22(4) Medical Science and the Law 275.

*** See for an explanation by defense attorney and professor Lawrence Taylor on how police instructions regarding “how to blow” may lead to inaccurate results.

**** Hlastula, M. Physiological Errors Associated with Alcohol Breath Tests. The Champion, 1985, 9(6). Quote available at