Breath Test Defenses

If you gave a breath test, you should know THE RESULTS ARE NOT 100% ACCURATE. There are many good defenses to breath test cases. Here are some of the defense that might apply to you:

Margin of error

No machine is 100% accurate. It is an inherent margin of error.


Partition Ratio

A partition ratio is a fancy way of saving it is a formula to convert breath alcohol concentration to blood alcohol concentration. Any number used is typically an average of different people. One of the leading blood scientists has held: “Obviously, there cannot exist a universal fixed blood/breath ratio of ethanol which applies for all subjects under all conditions of testing.[1]

Besides everyone having a different ratio, decreased lung capacity/shallow breaths can affect the results by as much as 50%[2].

[1]Jones at 14.

[2]Booth v. Director of Revenue, 34 SW 3d 221,223 (2000).


Temperature of your breath

A fever, or a woman’s menstrual cycle/menopause, can give higher than average body temperatures. Arguably, if someone is stressed, such as due to an arrest, their body temperature will also rise. When the body’s fight/ flight system is activated the muscles tense, heart rate and thevital organs speed up and as a result, blood flow is shunted from the extremities and directed to the vital organs to facilitate the increased level of arousal. As a result, changes of 5°, 10°or 15° can occur within just a few minutes[1]. If the officer says the person has a flushed face, you may also be able to argue an increase in body temperature.

Breathing Pattern

Similarly, breathing pattern can affect the BAC calculations. The subject's manner and mode of breathing just prior to providing a breath sample for analysis can significantly alter the concentration of alcohol in the resulting exhalation. A driver holding his breath for a short time (20 seconds) before exhalation can increase the alcohol concentration in exhaled air by 15%. Alternatively, hyperventaliting, lowers it up by to 20%[1].

As breath is expired from the lungs, the longer the person breaths, the higher the temperature of breath is. “The temperature of breath as it leaves the mouth rises from about 33.3 to 34.4°C as the volume of breath exhaled rises from 500 to 4500 ml”[2]. Accordingly, the person’s BAC should always be going up as the person continues to blow into the machine. If the officer says “blow, blow, blow”, he can artificially inflate the BAC, because the Intoxilyzer does not compensate for breath temperature, or use it as part of its calculations.

[1]Jones at 18

[2]Jones at 17


Mouth Alcohol

To get a valid BAC, the machine must know the alcohol concentration in your lungs. Alcohol in your mouth will not affect your BAC as the alcohol did not absorb into your blood. Mouth alcohol will always give a falsely high reading.

[1]People v. Bonutti, 788 NE 2d 331, 334(2003)

[2]Barone at 2-62.


GERD / Acid Reflux Disease

Similar to Mouth alcohol is Gastroesophageal reflux disease (GERD). Reflux means the stomach acids and other contents go back up through the esophagus into the throat and mouth. In healthy people the lower esophageal sphincter closes. In patients with GERD it does not. Alcohol, beer, wine, coffee, and drinks with carbonation can make the symptoms of GERD worse because they dilate the stomach and therefore dilate the lower esophageal sphincter[1].

Air from the stomach, is not the same as “deep lung air.”Accordingly, the result will be inaccurate. Because a person with GERD can have a constant flow of air, the slope detector will not notice the problem, as opposed to a spike by a burp.

One can be tested for GERD with an endoscopy. The photographs can be looked at to see if there is evidence of damage caused from the acid erupting. Further, photographs can determine if the Lower Esophageal Sphincter is open[2].

If you take medicine for acid reflux, this can also help to show you have GERD


[2]Barone at 2-62.


Operator Error

Even though the officer has training, they sometimes make mistakes in administering a breath test.


Testing During the Absorptive Phase

The absorptive phase is when alcohol is still being absorbed by the body from the stomach. All BAC levels will be inaccurate (in all likelihood higher) if the person is tested in the post-absorptive phase if he was in the absorptive phase at the time of driving. Studies by Kurt M. Dubowski indicate varying ranges of elapsed time from the end of alcohol intake to peak blood alcohol concentration of 14 to 138 minutes, 9 to 114 minutes, and 12 to 166 minutes[1]. He concludes:

“It is often impossible to determine whether the postabsorptive state has been reached at any given time. Those factors make it impossible or infeasible to convert the alcohol concentration of breath or urine to the simultaneous blood alcohol concentration with forensically acceptable certainty, especially under per se or absolute alcohol concentration laws.

However, specific to breath tests, “During the absorption phase and around the peak BAC breath analysis tends to overestimate venous BAC and the differences will depend on the actual blood/breath ratio for the person tested in comparison with the 2100 calibration factor and the magnitude of arterio-venous difference[3]One study showed a breath test result can be as much as 100 percent higher than the BAC level during the absorptive phase[4].

[1]Kurt M. Dubowski, Absorption, Distribution and Elimination of Alcohol:Highway Safety Aspects, 10 J. Stud. Alcohol Suppl. 98-105 (July 1985).

[2]Id. at 105

[3]Jones at 17

[4]E. Martin, W. Moll, P. Schmid, L. Dettli, The Pharmacokinetics of Alcohol in Human Breath, Venous and Arterial Blood After Oral Ingestion, 26 (5) Eur. J. Clin. Pharmacol., 619 (1984). As referenced at


One of the most well known blood experts in the country identifies the following problems with determining alcohol concentrations in breath:

"Phase of ethanol metabolism

Arterio-venous differences

Source of blood analyzed; arterial, venous, capillary

Blood hematology; hematocrit value, salt, fat, and protein content

Intra-pulmonary gas pressure

Ambient temperature and humidity

Expired-breath temperature

Breathing pattern; hypo-and hyper-ventilation

Bronchopulmonary disease

Presence of mouth alcohol

Regurgitation of stomach fluids

Phase of exhalation; end expiratory or top-lung air

Breath specimen; rebreathed, end-expired, mixed expired

Body temperature; hyperthermia-hypothermia[1]

Many of these defenses require an expert witness

[1] A. W. Jones, Physiological Aspects of Breath Alcohol Measurement, Alcohol, Drugs and Driving, Volume 6 Number 2, Pg. 15 (1990). Hereby referenced as Jones.