How Accurate Are Chemical Tests Used in DWI Cases?

How Accurate Are Chemical Tests Used in DWI Cases?The results of breath, blood, or urine tests are often presented in DWI cases as proof that the defendant was intoxicated while behind the wheel. But, these tests are not always accurate. Here’s what you need to know about the accuracy of chemical tests used in DWI cases:

Urine Tests

Most DWI experts would agree that urine tests are the least accurate of all three chemical tests. Why? The level of alcohol in a person’s urine is not the same as the level of alcohol in his blood. Some people have twice as much detectable alcohol in their urine than they do in their blood, while others have 40% more. Because it varies so much, it’s hard to determine whether or not someone is over the legal limit based on a urine test.

Blood Tests

Blood tests produce the most accurate results, but they are far from perfect. A blood test can produce inaccurate results if the sample is not handled properly or if the test is not administered correctly. For example, if preservatives are not added to the blood sample to keep it fresh, the results may show that the person was intoxicated even though he was not. Because of this, criminal defense attorneys must carefully review your case to identify errors that could have affected the results.

Breath Tests

A breath test is administered using a breathalyzer device, which is designed to measure the amount of alcohol in air exhaled from your lungs. Administration errors can affect the accuracy of a breath test’s results. For instance, if the law enforcement officer failed to properly calibrate the device, it may not produce accurate results.

Other factors can affect the accuracy of the results, too. Products that contain alcohol such as mouthwash or breath fresheners can skew the results of a breathalyzer test. As a result, someone who just took a swig of mouthwash may fail a breathalyzer test even if they haven’t had a sip of alcohol.

Chemical tests can help law enforcement officers identify intoxicated drivers, but they don’t always work in the way they were intended. For this reason, it’s important that DWI defendants do not give up hope simply because their test results show they were intoxicated at the time of their arrest.

If you have been charged with DWI, trust the skilled criminal defense attorneys at The Missouri DWI & Criminal Law Center at the Benjamin Law Firm, LLC. Our team will work tirelessly to weaken the prosecution’s case and reach the best possible in your case. Call our office at 816-322-8008, email us at or fill out our confidential online form to schedule a consultation today.

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