Texas expects its law enforcement officers to collect blood samples to confirm someone’s impairment after a traffic stop or an arrest for allegedly driving while impaired. Particularly in cases that involve death or injury to someone else in a crash caused by one driver, it is likely that police will want to draw blood from a driver they suspect may be under the influence of alcohol.

People often know that they have the right to refuse a breath test, even though that can result in additional consequences for them later on. It is common for people to assume that they also have the right to decline a blood draw by law enforcement, but that may prove a more difficult thing to do.

For years, Texas had a mandatory blood draw law, although the courts eventually threw out the statute, stating that those kinds of blood draws violated the Constitutional rights of the drivers involved. That means that, other than in cases where a driver is unconscious, police need to obtain either consent or a warrant for a blood draw related to a potential impaired driving case.

Officers have to get a warrant to draw blood without permission

You have the right to refuse a blood draw, but officers can then seek a warrant to compel you to submit to testing. Many impaired-driving arrests take place late at night or over the weekend. This may lead people to assume that they don’t have to worry about officers securing a warrant when the courts aren’t open.

However, it is straightforward for officers to secure a blood draw warrant in a suspected impaired driving case, regardless of the time of day at which the arrest occurs. While they can’t draw blood without a warrant unless you give them permission, it is likely that they can secure a warrant within two hours of the time of your arrest. That means they will have chemical evidence that meets the criteria to prove impairment to the courts.

You can still challenge evidence even after a blood draw

It is an all too common misconception among Texans that a blood draw that shows the presence of alcohol or other drugs is basically the end of your ability to defend against impaired driving allegations. People seem to believe that chemical tests are completely accurate and conclusive, leaving no room for reasonable doubt.

The truth is that chemical tests are not infallible, and the state of Texas can make mistakes with handling, transferring, storing and testing samples drawn from individuals. You may be able to question some of the evidence that the state uses against you due to gaps in the chain of custody and other issues.