Tuesday, July 16, 2024

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Texas DWI Blood Test Issues

Mimi Coffey DWI Lawyer, blood testThough many don’t realize it, most Texas DWI cases involve blood tests rather than breath tests. This is in large part because of the fact that the law allows police to draw your blood by getting a warrant if you refuse to give breath or blood. Regardless of whether police drew blood as a result of consent or a warrant, there are many issues surrounding the reliability of the result of a blood test. This is in addition to the requirements for blood draws in Texas DWI.


One of the main issues with blood tests is fermentation. The technical definition of fermentation is “the chemical process by which molecules are broken down anaerobically”. This can be described in simpler terms as the process where a substance metabolizes. Many people are familiar with the concept of fermentation related to making things like beer or wine. What many may not know is that blood can also experience fermentation. When a tube is old or defective, room air can get in and cause the blood to ferment faster. When blood experiences fermentation, it tends to result in a higher blood alcohol score.

For example, a fermented sample may return a result above .15 even though the actual alcohol content should be much lower. This is one explanation for why many people hear/see the blood result and say “I know I wasn’t that drunk”. Mimi has a background in science and has hands-on experience analyzing blood test results through education at Axion Labs and the UTA Shimadzu lab on gas chromatography. This is one reason why Mimi might request blood discovery for your case. What she finds in that discovery might show that fermentation or a host of other issues might be at play.

Other Blood Test Issues

There are a host of issues that can affect the reliability of the blood test or its result, including:

  • Fermentation (see above)
  • Contamination – for example, another substance mingles with the blood.
  • Misidentification – for example, placing the wrong name on the tube. This can also happen when placing incorrect information on the tube..
  • Improper Calibration – this occurs, for example, when the testers do not properly calibrate the machine used for testing.
  • Expired Calibration – when the machine used for testing is out-of-date.
  • Inaccurate Pipettes
  • Inaccurate Dilutors
  • Deficient Quality Control – when the technique is not properly supervised, or when the blood results are not double-checked before submission.
  • Improper venipuncture (see video) – in other words, when the technician does not perform the blood draw correctly.
  • Inaccurate calculations (at all levels including the calibration curve & margin of error). In other words, interpreting the data incorrectly.

See the below video for an example of proper blood draw procedure.

Mimi Coffey DWI Lawyer, blood test procedure

Mimi Coffey – DWI Defense Lawyer in Dallas County, DWI Lawyer in Tarrant County, DWI Lawyer in Wise County, DWI Lawyer in Johnson County, DWI Lawyer in Parker County, DWI Lawyer in Collin County, DWI Lawyer in Denton County


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Mimi Coffey

Mimi Coffey

Mimi Coffey is a trial attorney with 24 years experience. She is the founder of The Coffey Firm, serving Dallas, Tarrant and Collin counties. She is board-certified in DWI by the National College of DUI Defense (NCDD) and is a Regent of the NCDD. Mimi Coffey also listed on several “top” directory listings such as DWI attorneys Tarrant County, DWI Lawyer Fort Worth, DWI attorney Dallas County, DWI attorneys Collin County and DWI attorneys Parker County. I am very involved with the community DFW caring DWI lawyer, Texas Tech School of Law foundation and I enjoy using the skills I have developed to give back to the community. She has also appeared numerous times as a legal commentator for CNN, National Fox News, as well as local Dallas/Fort Worth stations on DWI-related stories. She is also a frequent speaker at both national and statewide seminars. She is a prolific trial attorney with a proven trial record. She has tried over 300 cases, with 80% of them being jury trials in her 18-year career. Her success includes everything from .21 breath tests, blood tests to 3 car accident cases just to name a few. Mimi’s cases have also made good case law for the State of Texas. For example, in Tarvin v. State, it was found that weaving within your own lane was not a traffic violation. In Lajoie v. State, the courts determined that the defendant’s request to have his attorney must be suppressed as opposed to used as evidence of guilt. She is the author of Texas DWI Defense: The Law and Practice. She is also the author of three nationally-published articles and four statewide articles. Mimi has twice attended Indiana University’s Borkenstein Course for state toxicologists both on alcohol and drugs. She has also completed the NHTSA SFST Course, SFST Instructor Course and the 12-Step DRE Mini-Course Program. She is also one of the first attorneys in the United States to attend the Axion Labs Gas Chromatography Training. Her minor in college was Geology lending her a comprehensive and disciplined scientific mind when it comes to scientific and mathematical issues such as blood and breath testing. Mimi has won the President’s Heart of a Champion Award presented by the Texas Criminal Defense Lawyers Association (TCDLA) numerous times. Mimi also led the effort to get the State Bar of Texas’ Board of Legal Specialization to recognize the NCDD’s DWI Certification. Mimi has been active in 4 legislative sessions in fighting against bad DWI laws. Her efforts prevented the breath/blood test refusal as being a separate crime. She has advocated for true deferred adjudication for DWI. Mimi also sued a Dalworthington Gardens police officer for illegally drawing blood. Since her lawsuit, the 2nd Court of Appeals ruled against police officers drawing blood. (The Court of Criminal Appeals overturned this). Mimi also sued the Texas Department of Public Safety for its double jeopardy surcharge program. Since the initiation of her suit, Texas DPS has instituted amnesty programs based on one’s earning potential.

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