Mistakes Can Occur During DWI Blood Test Process

 Posted on September 26,2018 in DWI / DUI

Mistakes Can Occur During DWI Blood Test ProcessThough more accurate than a breath test, a blood test can still have inaccurate results in a driving while intoxicated case. There are many chances for a blood sample to become contaminated during the process, resulting in the sample showing a higher blood alcohol concentration level than was actually in the driver’s blood at the time of the arrest. An experienced DWI defense attorney knows where errors are likely to occur in the blood test process that may make the test results inaccurate and inadmissible in court.

Blood Drawing

Mistakes in taking the suspect’s blood can contaminate the sample from the start. A police officer drawing your blood is not always as skilled as a medical professional. The officer may make a mistake by:

  • Waiting too long to draw the blood sample;
  • Contaminating the sample with the alcohol swab used to clean the extraction site on the skin; or
  • Drawing a blood clot, which has a higher concentration of blood alcohol than a normal blood sample.

You may need to recount possible mistakes made during the blood drawing process, as the person drawing the blood is not required to testify.

Blood Storage

Police usually send blood samples in a DWI case to a testing lab with the Department of Public Safety. If the samples cannot be sent immediately to the lab, they must be refrigerated to preserve their condition. Allowing the blood to become heated causes it to ferment, which will raise blood alcohol concentration in the sample. A blood sample that was not properly stored should not be admissible in a DWI case.

Chain of Custody

Several people will handle the blood sample during the testing process. The documentation of when and how the sample is transferred is called the chain of custody. Any breaks in the chain of custody can raise doubts about whether the sample was mishandled or contaminated. In an alarming recent example, a blood sample from a DWI suspect was inadvertently sent to a Texas attorney instead of a lab.

Testing Process

DPS labs use a machine called a gas chromatograph to test for alcohol levels in a blood sample. It is advisable to get a copy of the test report for yourself because the information is complicated and can be misunderstood. You should not allow the prosecution to present test results if a hospital conducted the test. A hospital does not have the equipment to accurately read the alcohol level in your blood because it is more concerned with knowing whether you have any alcohol in your blood.

Questioning Test Results

A blood test is not a definitive answer as to whether you were intoxicated at the time of your arrest. A San Antonio DWI defense attorney at the Law Offices of Sam H. Lock can contest results that were misinterpreted or may have come from a contaminated sample. Schedule your consultation by calling 210-226-0965.



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