Category: Science Behind DUI Testing

The Science Behind DUI Testing: Debunking Myths and Misconceptions – Guest Post


Science Behind DUI Testing

DUI testing is crucial for cracking down on drunk drivers and helping to make the roads safer for all, but there are a lot of myths and misconceptions about how DUI testing actually works, with some people suggesting that there are ways to cheat the test, for example.

In this guide, we’ll bust some of the most common DUI testing myths, explaining how testing really works and covering the key pieces of information you need to know if you’re ever pulled over and tested.

Types of DUI Tests

Before we get to the myths regarding DUI testing, it’s important to have a clear understanding of some of the different varieties of tests that the police may use to determine whether or not a driver is under the influence of drugs or alcohol.

Blood Tests

Blood tests are regarded by many experts as the most accurate type of DUI testing to determine a person’s blood-alcohol content (BAC). Drivers have to provide consent to have a blood test carried out, but refusing to give consent can result in the suspension of your license.

Breath Tests

Breath tests are the most common method used by police officers to check a person’s BAC. Typically, they involve the use of a breathalyzer device, which analyzes the contents of a person’s breath and can detect traces of alcohol in the breath.

Urine Tests

Finally, there are urine tests, which are considered the least accurate of the three and are only really used as a ‘last resort’. Urine testing can’t usually be performed right at the time of the stop, so it can be difficult to get a precise reading with this method.

Myths and Misconceptions Surrounding DUI Testing

Next, let’s look at some of the many myths and misconceptions around DUI testing, explaining why those myths are false.

Your Blood Alcohol Content Needs to Be 0.08 Percent or Higher to Get a DUI

This is a common myth that has spread across the US, but if you think that your BAC needs to be at least 0.08% to be charged with a DUI, this information is false. In reality, the chargeable BAC level varies from state to state, and officers can often arrest you if they feel that your abilities are impaired, no matter what your BAC happens to be.

If I Pass the Field Sobriety Test, I Can’t Be Charged with a DUI

Even if you pass the field sobriety test, there’s still a chance that the officer may arrest you. They may have other reasons to believe that you were driving under the influence, so passing the field tests is not at all a guarantee that you won’t be arrested.

DUI Testing Is Just a Way for the Police to Make Money

This is also not true. DUI testing is carried out for public safety, in order to reduce the number of drunk or drug-using drivers on the roads and minimize the chances of people being involved in dangerous or deadly accidents.

Law Enforcers Have to Catch You Driving to Arrest You for DUI

This one might sound logical, but it’s not true. While most DUI arrests involve officers catching and stopping people driving, law enforcement personnel can also arrest you and test you for a DUI if they see you parked and getting out of a vehicle.

You Can Trick the Breathalyzer by Sucking a Penny

This is a myth that has spread all over the world for many years, but there’s actually no truth to it. With modern breathalyzer devices, sucking a penny (or any other coin) has absolutely no impact on the results.

It’s Just a DUI Charge. I Don’t Need a Lawyer.

This is a common mistake that a lot of people make, and it can cause them to end up in far more trouble than they initially expected. Having a DUI defense lawyer on your side can make a huge difference in DUI cases and can help you avoid punishment or obtain a lesser punishment.

Accuracy of DUI Tests

The accuracy of DUI tests is often called into question, and it can be a key factor used by defense lawyers to help their clients avoid punishment. Even though these testing methods have a good degree of accuracy in general, their reliability levels can vary, and various factors may produce unreliable results.

Factors That Can Affect the Accuracy of the Test Results

There are multiple factors that can influence the results of DUI testing. For example, breathalyzer devices are not programmed to differentiate between the people taking them; they essentially operate on the assumption that every test subject is the same, and this can lead to inaccurate results, as a person’s job, lifestyle, or diet may impact their breath test results.

Medical conditions and medications may also affect DUI test results and even residual alcohol in the mouth from products like mouthwash or breath freshening sprays may be detected on a breathalyzer. Environmental factors, like the presence of paint or acetone, can also skew the results.

In addition. cannabis is a factor that can affect the accuracy of DUI test results as well. Cannabis use can impair a person’s ability to drive safely and can also impact their performance on field sobriety tests. The primary psychoactive compound in cannabis, THC, can remain in a person’s system for several hours or even days and weeks after use. This means that a person who has used cannabis may still test positive for THC in a DUI test, even if they are no longer impaired.

False positives and false negatives can occur in DUI tests, which can result in wrongful arrests or charges being dropped against impaired drivers. It is essential to ensure that DUI tests are administered accurately and reliably to prevent these errors.

How False Positives and False Negatives Can Occur

Even though testing devices and processes have a good degree of accuracy, they’re not flawless. False positives and false negatives can occur in DUI testing in several ways:

  • Breathalyzer errors: Breathalyzer tests are one of the most common methods for measuring BAC. However, these tests can be affected by external factors such as residual mouth alcohol, temperature, and other substances in the mouth. These factors can result in a false positive reading, indicating a higher BAC than what the individual actually has.
  • Blood sample errors: Blood tests are considered more accurate than breathalyzer tests, but they are not immune to errors. False positives can occur if the blood sample is contaminated or mishandled during the testing process. False negatives can occur if the blood sample is not taken correctly or is not tested promptly.
  • Field sobriety test errors: Field sobriety tests (FSTs) are physical tests that measure a driver’s coordination, balance, and ability to follow instructions. False positives can occur if the FST is not administered correctly or if the driver has a medical condition that affects their performance. False negatives can occur if the driver is able to perform the FST despite being under the influence of alcohol.

Overall, false positives and false negatives in DUI testing can have serious consequences, including wrongful arrests and convictions, as well as unsafe drivers remaining on the road. It is crucial for law enforcement agencies to ensure that the testing methods are reliable and accurate, and for drivers to be aware of their rights and the potential for errors in testing.

Field Sobriety Tests

As well as blood and breath tests, you may have to undergo field sobriety tests after being pulled over by police.

Purpose of Field Sobriety Tests

The purpose of field sobriety tests is to simply give the officers an idea of how intoxicated the individual may be. If an individual can’t perform basic tasks, like reciting the alphabet backward or standing on one leg, it’s usually a clear sign that they’ve got a certain level of alcohol in their system.

Common Field Sobriety Tests and How They Work

Some common field sobriety tests may include:

  • Balancing on one leg.
  • Walking along an imaginary straight line.
  • Reciting the alphabet backwards or forwards.
  • Solving a basic math problem.
  • Following an object, like a pen, with your eyes.


As we can see, there are many myths around DUI testing, and many people take drunk driving less seriously because of some of those myths. We hope that this guide has helped to debunk some of the common misconceptions you may have around DUIs, as it’s important for everyone to be aware of the risks and realities of drunk driving and DUI testing.