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Four things that can affect the results of your breath test

Breath tests have become the golden standard in just about every state in the country, including here in Illinois. Not only do they allow police to determine a driver's level of impairment immediately following a traffic stop (oftentimes right there on the side of the road), they are less invasive than blood tests (and less likely to violate a person's constitutional rights as well).

Unfortunately, as paper written by a doctor at the University of Washington's Division of Pulmonary and Critical Care Medicine points out, these tests haven't gotten any more accurate over the past few decades despite advancements in technology. Furthermore, numerous studies have concluded what many defense attorneys have been saying for years: these tests aren't as accurate as police and prosecutors think.

Here are just four factors that can affect a breath test result:

Alcohol is more soluble in water than air

You may not realize it, but the humidity in your breath and the air around you could have a significant impact on a breath test reading. That's because alcohol is more soluble in water.

As the University of Washing paper explains, "The very high solubility of alcohol in water guarantees its strong interaction with airway tissue," meaning a hot, humid day could yield a higher blood-alcohol concentration (BAC) reading than if the weather conditions were hot and dry.


Breath volume isn't taken into consideration

The general assumption is that you will blow the same BAC regardless of how much air you blow into a breath test. Unfortunately, this simply isn't true. The volume of air pushed into a device does matter.

By design, the air exhaled in the beginning part of your breath typically has a lower BAC reading than the breath measured in the middle or end. If testing devices take the average of the entire breath, but the breath was relatively low in volume, you could see a lower average reading than if you had provided a larger volume sample.


Breathing patterns can reduce or lower BrAC

Your breathing pattern can also impact the results of a breath test, Dr. Michael P. Hlastala points out in his University of Washington paper. As he explains, hyperventilating and breathing deeply can reduce the breath alcohol concentration (BrAC) by 11 percent and 4 percent respectively while holding your breath can actually increase the BrAC reading by 6 to 12 percent.

50 percent margin of error

Perhaps the most damaging factor in the breath-test accuracy debate is the fact that breath tests can have a margin of error of up to 50 percent, concludes an article for the National Motorists Association. This can be incredibly problematic for drivers because a .1 reading can actually mean a BAC of anywhere between .05 and .15. A variability of this magnitude could mean the difference of a DWI/DUI or no charges.

Although it's important for police to identify when a person is impaired, Breathalyzer tests results should not be the only deciding factor in a case. Because of the four factors above, they may not be as accurate as we think, which means some people may receive DWI/DUIs when they aren't warranted.

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