Blood Alcohol Testing

In the defense of a DWI case, the first and most important consideration is the driver‘s alcohol levels.  Under the New Mexico Implied Consent Act, a driver must submit to a blood or breath test upon the request of the officer or face revocation of his or her driver‘s license.

While the most common method for measuring a driver’s alcohol content is breath analysis, or more commonly a breathalyzer, a blood test is also an option.  In fact, blood tests are generally considered more accurate than breath tests.

Accuracy of Blood Tests

However, the truth is that no one really knows how accurate blood alcohol testing is. Most crime labs claim to be accurate within 5%. Their accuracy claim means that if a driver’s blood result is .08%, the test’s true result could be anywhere between 5% lower or 5% higher. Other scientific organizations, including the American Academy of Forensic Sciences, do not believe that 5% is a realistic range of accuracy and state that the true range is likely closer to 10% higher or lower.

While a 5% difference does not seem like much, it can be very significant. After all, if the crime lab testing indicates that a driver’s blood alcohol level was .08%, then even a small margin of error could mean that the driver’s blood alcohol level was actually below the legal limit.

Blood Alcohol Measurement Processes and Problems

The process of determining the amount of alcohol in driver’s blood is very complicated and requires the use of sophisticated lab equipment called a gas chromatograph. The gas chromatograph vaporizes the blood sample, which allows it to separate and analyze the different compounds in the blood.

There are many different problems that can occur with a blood sample that will affect the accuracy of the blood alcohol testing. Blood must be drawn, transported and stored properly. For example, if the person drawing the blood uses an alcohol swab before taking the sample, the sample may be contaminated. The blood must also be stored at a proper temperature or the testing may not provide a correct reading. In addition, while it will not necessarily affect the test’s accuracy, New Mexico law requires that for blood alcohol testing the blood must be drawn by a physician, licensed professional, nurse or laboratory technician. Therefore, if any other person draws blood it may not be admissible in court.

Presentation of Blood Test Results at Trial  by the State

In the past, at trial for driving under the influence a prosecutor would call a witness from the crime lab where a driver’s blood was tested. The crime lab worker would then testify that the driver’s blood alcohol content was at a certain level, and that the level was higher than the legal limit of .08%. All that has changed now.

The United States Supreme Court reviewed the issue in the case of Bullcoming v. New Mexico. The Supreme Court determined that an accused drunk driver has a 6th Amendment allows for confrontation of witnesses in criminal trial the actual person who tested his or her blood in the crime lab. As a result, the prosecutor cannot simply call any person from the crime lab where the blood was tested.

Instead, the prosecution must call the actual person who conducted the blood testing to ask about the results of the testing, because human error is a distinct possibility with blood alcohol testing. By requiring the lab analyst who conducted the blood testing to appear, the defense attorney now has an opportunity to question the analyst about the exact procedure he or she used to conduct the testing.

As mentioned in the opening, the breath or blood alcohol level is the most important first consideration in a DWI case. It is important to have an attorney experienced in DWI defense who can discuss all the circumstances of your blood test to determine the best line of defense in your case.


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