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What Can Skew the Results of Blood and Breath DUI Tests?Though not the only form of evidence in a case of driving under the influence, the results from a chemical sobriety test can strongly support the claim that you were legally intoxicated at the time of your arrest. Unlike observations of your behavior, courts view the blood or breath test results as objective evidence because they measure your blood alcohol concentration and detect illegal substances in your body that may have impaired you. However, testing above the BAC limit does not always mean that you were intoxicated. Your DUI defense attorney will look into possible reasons why the test results may be inaccurate.

Breath Tests

During a traffic stop, a police officer who suspects that you are intoxicated may ask you to provide a breath sample using a portable device, such as a Breathalyzer. Breath tests are quicker and easier than blood tests but are also more prone to error:

  • Residue from substances such a mouthwash and breath fresheners may have trace amounts of alcohol in them that skew the test results.
  • The presence of nearby chemicals such as paint or adhesives can cause false results.
  • The test uses hardware that must be regularly calibrated to ensure accuracy and software that may be vulnerable to glitches.
  • The officer should conduct the breath test multiple to see that the results are consistent.

Blood Test

A police officer is more likely to take a blood sample at the police station or a hospital if you are being treated for injuries. While a blood test is considered the more accurate chemical sobriety test, there is still a possibility of inaccuracies:


Appeal Ruling Questions Constitutionality of DUI Testing LawAn Illinois appellate court recently overturned a man’s conviction for first degree murder, aggravated driving under the influence and failure to report a motor vehicle accident involving a death. There were several reasons that the court decided to send the case back for retrial:

  • The jury should have been instructed of a possible lesser charge of reckless homicide as an alternative to first degree murder;
  • The class 1 felony count of failure to report should not apply because it requires 30 minutes to have passed and the defendant was arrested about 10 minutes after the incident; and
  • Blood and urine samples should have been inadmissible as evidence because they were obtained by force and without a warrant.

The third point is potentially the most consequential because it questions the constitutionality of an Illinois law that allows police officers to force a suspect to give bodily fluid samples after a DUI arrest.

Case Details


traffic stop rights Illinois police, McHenry County criminal attorneyDriving under the influence (DUI) is one of the most politicized crimes in the United States. Politicians have completed a large amount of work to get the votes of people who have been impacted by drunk drivers, and most of this work has involved making DUI laws extremely draconian. As DUI laws have become stricter, however, implied consent laws have had to keep pace, or else DUI suspects would opt for their lower penalties, rather than face the overwhelming penalties of a DUI conviction.

In some states, politicians even chose to make an implied consent violation – the refusal to take a blood-alcohol content (BAC) test – an actual crime, rather than just an administrative violation.

However, as one recent Supreme Court case has shown, this has taken implied consent laws so far that they now implicate your Fourth Amendment rights.

Illinois State Bar Association State Bar of Wisconsin Crystal Lake Chamber of Commerce Illinois Trial Lawyers Association McHenry County Bar Association
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