Are the Results of my Breathalyzer Test Accurate?


In Massachusetts, there is an implied consent law. This means that the law presumes that every time you drive a vehicle in the Commonwealth, you are consenting to a Blood Alcohol Concentration test, usually with a device known as a “breathalyzer,” if there is reason to suspect that you are intoxicated.  This does not mean that you must allow the police to conduct the test. You can refuse it.  If you do refuse the test, your license will be suspended.  If you take the test, the results of that test can be used against you in court. Anything over .08 is, according to the law, a per se violation of Massachusetts law.

In order for you to understand how we can challenge these tests you need to know a little bit about how they work in the first place. Alcohol that a person drinks shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol is not digested upon absorption or chemically changed in the bloodstream. As the blood goes through the lungs, a physiologically predictable amount of the alcohol moves across the lung membranes and into the lungs themselves. Once in contact with the air in the lungs, it evaporates and is exhaled. The concentration of the alcohol in the lungs is directly related to the concentration of the alcohol in the blood. The ratio of breath alcohol to blood alcohol is generally 2100 to 1 (and called the partition ratio), so the alcohol content of 2100 milliliters of exhaled air will be the same as for 1 milliliter of blood. The math is simple from there and leads to blood alcohol readings expressed as a percentage of alcohol in the blood.

This math formula is just a generalization, however, and is not accurate in every case. The actual partition ratio can vary between 1700 and 2400 depending upon the individual and local environmental conditions, which can result in a breathalyzer reporting either a higher or lower calculated blood alcohol reading. This means that the machine will read the same blood alcohol content for a ninety-pound person as it will for a three-hundred pound person. You can see why the results can be misleading.

However, the fact that the machine does not account for the difference in weight and size of test subjects is not the only reason that these test results are unreliable. Body temperature can affect the results. Similarly, as you may have noticed above, the breathalyzer test measures blood from air that is exhaled not from blood. This means that things like bloody gums, burping, vomiting, hiccupping, or sneezing can all drastically change the results of the test. There is also something called “mouth alcohol.” This is alcohol retained in the mouth that measures on the test but does not accurately reflect blood alcohol content. Things like mouthwash and toothpaste can drastically change the results of these tests. Certain medical conditions and medications can impact the test results. Finally, the length of time between your last drink and when the test is conducted can impact the test results. Someone who drank a glass of wine five minutes before the test may have a higher blood alcohol content breathalyzer reading than someone who drank five shots of whiskey one hour before the test, and that’s not even accounting for all of the other factors listed above.

Breathalyzer machines are so notoriously ineffective at accurately determining your blood alcohol concentration that Massachusetts law requires the police to allow you to obtain independent test results. When a driver is arrested and requested to take the breathalyzer test, the police must provide a notification of rights to you in writing. That notice instructs the driver that he or she is entitled to be transported, within a reasonable period of time, to a medical facility to have their blood tested by a medical professional.

The bottom line is that most people believe that breathalyzer machines are fair and accurate, but they are not. You should not decide to plead guilty because you assume that the test results are accurate. Call a KJC Law Firm attorney today to discuss the details of your case.

There are also a number of ways in which the test results can be thrown out of court entirely so that the evidence cannot be used against you at all. Learn more about that here.

If you or a family member has been charged with OUI, call KJC Law Firm for a free consultation. We will tell you whether you have a defense and help you fight your case. KJC Law Firm has more than 125 years of experience litigating major cases, including numerous criminal defense cases in general, and OUI cases specifically. We have the resources to investigate your claim, hire the necessary experts, and get you the justice that you deserve. KJC Law Firm represents people accused of crimes from communities across Massachusetts, including the Greater Boston area, Cambridge, MetroWest, Worcester, Springfield, Cape Cod, Fall River and Lowell.

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