The Breathalyzer test has become the standard roadside and police station test for determining blood alcohol levels. However, the results of a Breathalyzer test are not irrebuttable evidence for or against a blood alcohol content over the legal limit of 0.08 percent.
If the Breathalyzer test is administered at the police station, usually a minimum of one hour after the arrest, the test cannot have measured the blood alcohol content (BAC) at the time of driving. Consumed alcohol takes between 45 minutes and 2 hours to be absorbed into the bloodstream, while normal metabolism decreases BAC thereafter. Thus, taking a Breathanalyzer test too soon will result in more false negatives, while waiting too long will result in more false positives.
For this reason, a Breathalyzer result under 0.08 percent, taken an hour after the time of arrest, is not irrebuttable evidence that the BAC at the time of driving was not over 0.08 percent. Although the Breathalyzer reading will be offered as evidence during criminal proceedings in most states, the legal issue is the BAC while driving. Since a blood alcohol curve cannot be extrapolated from a single Breathalyzer reading, most attempts to retrograde extrapolate BAC using the Widmark factor can be easily rebutted. The jury is usually instructed to disregard Breathalyzer evidence if it contradicts other evidence obtained at the scene, such as the video from a police cruiser or the results of field sobriety tests.
Breathalyzer testing is designed to estimate BAC based on a breath sample. However, in clinical tests, only a third of Breathalyzer results are within 0.01percent of measurement of BAC by blood analysis. South Dakota law accepts only blood analysis for evidentiary use, with all types of Breathalyzers being limited to preliminary screening use only.
Breathalyzer measures of BAC rely on baseline breathing patterns and cell volumes of blood, or hematocrits. Faster breathing patterns or hyperventilation, especially as a result of vigorous exercise, can decrease Breathalyzer readings by as much as 30% without actually changing BAC levels. The lower the hematocrit, the higher the Breathalyzer reading. Men tend to have higher hematocrits on average than women, making it more likely that they will pass a preliminary Breathalyzer test.
All Breathanalyzers are not created equal. Breathanalyzers which are on the Conforming Products List are approved for evidentiary use. All other types of Breathalyzers can only be used for preliminary screening, and their results are not admissible as evidence. Older models of Breathalyzers have problems distinguishing ethyl alcohol from substances with a similar molecular structure such as acetones, which are frequently found in naturally high levels in diabetics and dieters. Metered dose asthma inhalers have also been found to interfere with Breathalyzer measurement. Something as innocuous as Listerine can skew the readings into “lethal” levels. However, non-specificity issues will tend to produce false positives rather than false negatives.
Injury can skew Breathalyzer readings or even affect roadside sobriety tests without actually impacting on sobriety. Sudden release of pockets of occluded blood may artificially raise or lower BAC. Prescribed medication may result in inner ear imbalance which interferes with one of the three federally approved field sobriety tests: heel-to-toe, one-leg stand, and horizontal gaze nystagmus. Even as simple a matter as having to perform a one-leg stand on an uneven surface could skew field results. Know your rights, and don’t hesitate to call a lawyer specializing in DUI if you are charged with a DUI offense.