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Blood and Breath Tests

What you need to know about DUI blood alcohol tests and breath tests

Before police officers can make DWI arrests, they must establish that a driver's blood alcohol concentration (BAC) is .08 or higher. Officers used two types of tests that may be used later as proof that a driver was operating under the influence of alcohol.

Blood alcohol test

A blood alcohol test, conducted under the rules of the Texas Transportation Code, is one way of determining the amount of alcohol in your system. The test is administered by drawing a blood sample from the driver to determine the amount of alcohol in the body. While blood tests generally are more accurate than breath tests, blood alcohol tests still can be found to be inaccurate in some cases and can be challenged in court.

If you have been pulled over for DUI and think you may be intoxicated, do not volunteer to take a blood alcohol test at the police station, because you may help the prosecutor build a stronger case against you.

On the other hand, if you are suspected of drunk driving but did not have anything to drink, ask to take the test. The results may clear you of any charges.

The test is administered at the request of a law enforcement officer. The test also must be given by a qualified technician, doctor, chemist, registered nurse or licensed vocation nurse in a sanitary place. Typically, the blood test is administered at a hospital by a nurse. The blood, after drawn into a tube, must be refrigerated.

The results may be inaccurate for any number of reasons and an experienced attorney can raise questions, such as:

  • Was there blood contamination?
  • Were the blood samples switched?
  • Was the sample properly refrigerated?
  • Was there blood fermentation, which can lead to a higher alcohol level?

Breath tests

Breath tests are administered by blowing into the mouthpiece of a device called an Intoxilyzer. Texas uses the "Intoxilyzer 5000" or the "Intoxilyzer 5000en," depending on the county. The device works by measuring the amount of light that is absorbed in a particular substance (spectroscopy method). A high concentration absorbs more light and leads to a higher readout. The machine computes the light absorption into a BAC value. If the concentration is .08 or greater, the officer can arrest you for DWI.

There are many reasons why the Intoxilyzer may not be an accurate measurement of your BAC:

  • The officer may not be properly trained in how to use the machine.
  • The machine may not have been calibrated properly.
  • The machine may be a defective or malfunctioning Intoxilyzer.
  • The machine has a rate of error of .02 allowable between two breath specimens.
  • The device cannot measure what your BAC was at the time of driving.
  • The machine may give a false reading because it detects non-alcoholic substances in your body.
  • The machine may give a false reading because of a burp.
  • Another user may have contaminated the machine.

Having a Houston Area DWI defense attorney who is trained to know (and, where appropriate, to attack) the breath machine's limitations and weaknesses is the first priority if you decide to fight your Texas DWI case in court.

Contact a DWI defense lawyer in Texas

Amanda Webb - DWI Lawyer in the Houston Area is skilled at successfully challenging evidence used by prosecutors to convict suspects in drunk driving cases. We can stand up for you and aggressively protect your rights. Call 1-800-395-5951 for a free consultation.