In Texas, when you are suspected of DWI, an officer has the "option" of asking you to submit to a breath or blood test. You are allowed to refuse both tests, but an officer may attempt to obtain a warrant for your blood from a judge. To issue a warrant, the judge must find that there is probable cause to believe you were driving while intoxicated. If a warrant is issued, you do not have a right to refuse the collection of your blood for blood alcohol analysis. While you must comply with a warrant, you can challenge a warrant that is issued without probable cause.
We recommend that you do not consent to a blood draw - even when pressured with the fact that the police will "go get a warrant anyway." Let them get a warrant - there's a decent chance the judge may refuse to sign the warrant even if the police ask them.
There are several factors that can interfere with a blood test. For example, if the person drawing your blood wipes your arm with an alcohol swab, creating an artificially high blood alcohol level. Furthermore, if there are improper levels of preservative in the tube used for drawing your blood, the blood sample can actually ferment, creating alcohol.
We sometimes have our clients’ blood samples independently tested to verify that the results were accurate.
Also, even if a blood sample was properly drawn and stored, it’s important to note that while chemical testing may be accurate to determine blood alcohol content (BAC) at the time of testing, it is not conclusive evidence of BAC at the time of driving. It is not illegal to be above the legal limit while in a police station; the crime is driving while intoxicated, or driving above the legal limit, not having a BAC above the legal limit at a later time.