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How Accurate Are DUI Tests?

Law enforcement officers employ a variety of tests to assess a driver’s impairment before determining whether they are fit to operate a vehicle. Among the initial assessments is the field sobriety test, a set of evaluations designed to gauge a driver’s balance, coordination, and cognitive abilities. Tasks such as walking in a straight line, balancing on one leg, and tracking a flashlight with one’s eyes (known as the horizontal gaze nystagmus test) constitute common components of this assessment. Failure in these tests may prompt officers to pursue more precise methods for establishing inebriation. However, the question arises: how accurate are these commonly used drunk driving tests?

One of the most reliable methods for identifying drunk drivers is through blood tests. In most cases, blood tests can precisely reveal the extent of a driver’s impairment. Nevertheless, certain aspects of the test may be susceptible to errors. For instance, if a blood sample is improperly preserved, it could coagulate and decompose, rendering accurate readings impossible. Additionally, there is a risk of mix-ups or contamination if proper protocol is not followed, potentially compromising the reliability of the results.

Here are some additional points and considerations:

Blood Testing

  1. Accuracy: Blood tests are generally considered more accurate than breath tests in measuring the actual alcohol content in the blood. They precisely measure the BAC at the time of the test.
  2. Potential Issues: As mentioned, handling the blood sample can lead to accurate results. Contamination or mix-ups in the lab may compromise the integrity of the sample.

Breath Testing

  1. Convenience: Breath tests are convenient for on-the-spot testing during a drunk driving investigation. They are commonly used during traffic stops to assess a driver’s potential impairment quickly.
  2. Variability: Breathalyzers estimate BAC by measuring the alcohol in exhaled breath, which may not directly correlate with blood alcohol levels for everyone. Factors like body temperature and respiration rate can affect results.
  3. False Positives: Breathalyzers can produce false positives, especially if someone has recently used substances containing alcohol, like mouthwash or certain medications.

Legal Implications

  1. Implied Consent: Many jurisdictions, including Colorado as mentioned, have implied consent laws. Refusing to take a blood or breath test may result in consequences such as license suspension.
  2. Legal Representation: Seeking advice from a DUI attorney is important if you are arrested for drunk driving. They help you through the legal process and help you understand your rights and options.
  3. Refusal Consequences: While refusing tests may lead to license revocation, it’s essential to note that this varies by jurisdiction. Some places have more severe penalties for test refusal than others.

In summary, both blood and breath tests have their pros and cons, and the choice of which to administer often depends on the circumstances and available resources. Individuals should be aware of the potential limitations and legal implications of both testing types. If facing legal issues related to drunk driving charges, consulting with a legal professional is crucial for proper guidance.


The accuracy of DUI tests remains a subject of scrutiny and debate within the legal and scientific communities. While technological advancements have led to the development of various testing methods, questions persist regarding their reliability and potential for errors. The effectiveness of breathalyzer tests, blood tests, and field sobriety tests in accurately determining a driver’s level of impairment is influenced by various factors, including calibration precision, administration protocols, and individual variations. Thomas & Ahnell, LLC, a prominent legal firm specializing in DUI defense, recognizes the complexities surrounding DUI testing and emphasizes the importance of a thorough examination of the evidence to ensure fair and just legal outcomes. As the legal landscape continues to evolve, ongoing research and critical analysis are essential to refine and improve the accuracy of DUI testing methods.

Do you have further questions or concerns? Call us or contact the attorneys at Thomas & Ahnell, LLC, and we will be happy to help.

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