On April 17, 2013 the U.S. Supreme Court in Missouri v. McNeely answered the question of whether police can obtain a nonconsensual warrantless blood sample from a person accused of DUI. The answer is Yes, police will have to get a warrant first (most times).
The court held “that in drunk-driving investigations, the natural dissipation of alcohol in the blood stream does not constitute an exigency in every case sufficient to justify conducting a blood test without a warrant.
Whether a warrantless blood test of a driver suspected of DUI is reasonable will be determined case-by-case using the “totality-of-the-circumstances.”
The government was seeking a per se rule, contending that exigent circumstances exist when an officer has probable cause to believe that a person has been driving under the influence of alcohol because BAC evidence is inherently evanescent. Therefore, providing an exception for the need to secure a search warrant to conduct a blood draw.
The court noted a variety of circumstances that may give rise to an exigency sufficient to justify a warrantless search such as, law enforcements need to provide emergency assistance to an occupant of a home, Michigan v. Fisher, 558 U.S. 45, 47-48 (2009), engage in “hot pursuit” of a fleeing suspect, United States v. Santana, 427 U.S. 38, 42-43 (1976), enter a burning building to put out a fire and investigate its cause, Michigan v. Tyler, 436 U.S. 499, 509-510 (1978), to prevent the imminent destruction of evidence. See Cupp v. Murphy, 412 U.S. 291, 296 (1973); Kerr v. California, 374 U.S. 23, 40-41 (1963).
Despite the fact that a persons BAC level declines until the alcohol is eliminated, the Court should not depart from a careful case-by-case analysis of the exigency. When officers can reasonably obtain a warrant before having a blood sample drawn without significantly undermining the efficacy of the search, the Fourth Amendment mandates that they do so. See McDonald v. United States, 335 U.S. 451, 456 (1948).
Blood testing is different in critical respects from other destruction of evidence cases. A blood test conducted in a medical setting by trained personnel is less intrusive than other bodily invasions; this Court has never retreated from its recognition that any compelled intrusion into the human body implicates significant, constitutionally protected privacy interests.