Can a Blood Test Be Challenged in Court?

Yes — Blood Tests Are Challenged Regularly in Travis County DWI Cases

Blood draws in Austin DWI cases are typically analyzed at the Travis County Medical Examiner’s toxicology laboratory. The complete chain of custody — from the venipuncture through the lab analyst’s report — must be documented at every link. We request the complete lab file, not just the summary result, on every blood draw DWI case in Travis County. The complete file includes collection documentation, phlebotomist qualifications, tube type, preservation records, storage logs, analyst certification, and gas chromatograph calibration records.

The Blood Draw Warrant

APD routinely obtains blood draw warrants under Transportation Code §724.017 when defendants refuse the breath test. The warrant must be supported by probable cause. If the warrant lacked a sufficient factual basis, the blood draw itself is an illegal search and the results are suppressible under the Fourth Amendment.

Phlebotomist Qualifications

Under Texas Transportation Code, a blood draw must be performed by a physician, qualified technician, chemist, registered nurse, or licensed vocational nurse. If the person who drew the blood did not hold a qualifying certification at the time of the draw, the evidence may be inadmissible.

In Vitro Fermentation — The Post-Collection Problem

Improperly preserved blood samples can ferment after collection, producing additional ethanol not present at the time of the draw. If the sodium fluoride content in the collection tube is insufficient, or if the sample was stored at elevated temperature, the BAC measured at the lab can be higher than the actual BAC at the time of the draw. We examine preservation documentation on every Travis County blood draw case.

Chain of Custody Documentation

Every transfer of the blood sample between the collection site and the lab analyst must be documented. A gap in the chain of custody documentation — an undocumented transfer, missing refrigeration log, or absent lab receipt record — creates a challenge to the integrity of the evidence. See our full BAC and breath test defense page.

What to Do After a Blood Draw DWI in Austin

Call 512-599-9999 immediately. The time between the blood draw and the lab analysis is where preservation issues develop. The earlier we are involved, the more complete the chain of custody challenge we can build.