BAC tests are not always reliable

If police recently pulled you over with the suspicion of driving under the influence of alcohol, they probably asked you to perform a number of field tests to determine if you were impaired. If you had difficulty with any of these challenges, the officer may have asked to test the level of alcohol in your blood system.

There are three different tests law enforcement uses to estimate how much alcohol you had to drink. The tests have varying levels of reliability:

  • Least accurate: Urine test
  • Sufficiently accurate: Breath test
  • Most accurate: Blood test

Police may have required you to submit to more than one so that they had a close approximation of your true blood alcohol content.

Testing for alcohol in your urine

The urine test is the least accurate of the three types of BAC tests, and if police asked you for a urine sample, it may have been because the more reliable tests were not available. It is easy to dilute or substitute urine samples, and many other factors can affect their accuracy.

One reason why police do not prefer the urine test is that they cannot administer it during a traffic stop. By the time they completed your field sobriety tests, officially placed you under arrest and transported you to the police station, significant time may have passed, which can affect the accuracy of the sample.

Alcohol stays in your system between six and 24 hours, so a positive result does not necessarily prove that you were intoxicated at the time you were arrested.

The most convenient BAC test

For law enforcement, the breath test gives a quick and reasonably accurate measure of the alcohol in your blood, and the police may have used it to establish probable cause for your arrest or to get a warrant for a blood draw.

However, the presence of some environmental factors can affect the precision of a breath test, such as:

  • Paint thinner
  • Glue
  • Gasoline
  • Your diet

Breathalyzers work by measuring the alcohol that passes through the air sacs in your lungs. Since alcohol is absorbed into your blood and not digested, the level that is in your breath is similar to that in your blood, so the results are generally admissible in court.

Blood tests are the most accurate and the most invasive

Some states allow drivers to refuse blood tests in favor of less invasive breath or urine tests. However, in Wisconsin, you must submit to the blood test if police have a warrant. If you refused during your traffic stop, your driver's license may have been automatically suspended, and you may face even harsher penalties if you are ultimately convicted.

At the police station, an officer may have drawn your blood and sent it to a lab for analysis. Here is where human error can influence the accuracy of the test. At any point in the process - from the cleanliness of the vials to the temperature of the storage units to the attention paid to the correct labeling of your sample - a mistake or mishandling could render your sample unreliable.

An attorney with experience in OWI cases will certainly know the drawbacks of each BAC test and even more ways to challenge the results in court. Just because your test results may have shown your BAC to be .08 or higher does not mean your case is closed. Your attorney will fight to protect your rights and reduce the possibility that you will face harsh penalties.

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