The goal of law enforcement when officers suspect someone is guilty of driving while intoxicated is to gather as much evidence as possible. They want the prosecution to have the proof necessary to secure the conviction of someone who drives impaired. However, the methods they use may seem questionable, or even invasive, to some people.
According to the Texas Penal Code, whether an officer can request a mandatory blood draw depends on a variety of circumstances.
Implied consent
Even though drivers may never say, “I give you permission to take a blood sample,” the law still considers them to have provided implied consent if law enforcement has enough evidence of DWI to arrest them.
After the arrest, the officer has the authority to take a blood or breath sample, but he or she must inform drivers that they have the right to refuse. There are consequences for refusal, however, and the officer must also provide this information. A refusal results in an automatic license suspension for at least 180 days. Even after the refusal, an officer may still be able to get a warrant from a judge to order a blood draw.
An accident
After an accident involving injuries or death, an officer may arrest a driver he or she has reasonable grounds to believe the crash was DWI-related. In this case, the officer may request the blood draw or other chemical test. If the driver cannot respond to the request because he or she sustained injuries or died in the accident, the officer may order a blood test without formally requesting it from the driver.
Texas statute 724.017 explains that officers may not take blood samples, themselves. Only doctors, nurses, emergency medical technicians or other qualified health care professionals may perform blood draws, and they must do them in a sanitary place.