Even a Perfect BAC Test Has an Error Rate


The state of Texas takes intoxicated driving seriously. If you are convicted of a drunk driving offense, you will find yourself facing harsh penalties. Under Texas law, a blood alcohol concentration (BAC) of 0.08 or more is considered to be above the legal limit. This is where it is important to note that measuring a person’s BAC is not an exact science, at least not with the field sobriety tools police officers use at their disposal. To get an accurate reading, law enforcement officers must be sure that they have conducted the test in the proper manner. However, even when police officers do everything right, BAC tests still have an error rate. To be sure, this may be helpful in beating a DWI charge.

Understanding the Margin of Error

In a Texas DWI case, prosecutors can present many different types of evidence, from witness statements to the responding police officer’s report. Of course, in many DWI cases, the core piece of evidence is comprised of the results of a BAC test. To be relied on by the court, the BAC test must have been conducted in the approved manner, ensuring no contamination, interference, or any other type of serious flaw. However, a test that was correctly performed does not necessarily prove that the results are accurate. It is important for people to understand that all BAC testing Instruments have a margin of error.

BAC testing is not an exact science. This is especially important when you are dealing with the results of a breath test. Breathalyzers do not directly measure a person’s blood alcohol concentration; they estimate it. That is certainly not to say that a breath test is wholly inaccurate.That being said, these tests always have a margin of error. For example, imagine that a specific BAC test has an error rate of (+/- 0.01) when it is performed perfectly. If you took this test, and your BAC measured at 0.08, that means that your true BAC could be anywhere from 0.07 (below the legal limit) to 0.09 (above the legal limit). There is a substantial amount of uncertainty.

Texas Law: The BAC Margin of Error is Admissible Evidence

In Texas courts, BAC test error rates are considered to be admissible evidence. The error rate will be viewed along with all of the other evidence in order to assess the overall credibility of the test result. As a general rule, this means that the error rate is most relevant in cases in which the defendant is just over the legal limit, or has recorded a result just high enough for the prosecution to seek Class A misdemeanor charges. In these types of cases, it will be very important for the court to hear exactly how the BAC test was conducted so that a reasonable error rate can be calculated.

You Need to Protect Yourself Against BAC Test Errors

Texas prosecutors have an obligation to prove a defendant’s guilt beyond a reasonable doubt. If you can prove that there is a reasonable possibility that your supposedly ‘positive’ BAC test results were within the range of error, you may be able to beat a DWI charge. If you have been charged with intoxicated driving, you should be represented by an experienced Austin DWI defense lawyer who can review your case for this issue and help you build the strongest possible legal defense.