If an officer arrests a person for an offense under Chapter 49 of the Texas Penal Code involving the operation of a motor vehicle or water craft for suspicion of operation while intoxication then there may be a blood draw to determine the blood alcohol concentration level.
The key is that the officer must have placed the person under arrest prior to requiring a mandatory blood sample, however, failure to tell the suspect explicitly that he is under arrest may not automatically invalidate the blood sample. In Nottingham v. State, the Austin court found that reading the DIC-24 warnings constitutes evidence that the arrest element was met because even though the officer testified he did not arrest the suspect, the DIC-24 says in the body of the warning that the suspect is under arrest.